So, basically I'm trying to a build a gaming PC with as small budget as possible. I don''t usually do this kind of stuff and the reason why I'm building it, is to be able to play Cottage Simulator and My Summer Car. I'm not playing them myself, but it's for the teens to play with.

It seems that used PC's with recommended performance are around here 550€ and up, but I'm targeting to spend more like 150€ max., though it's not set in stone.

Technically you can find used PCs with first and second gen Intel i7 and GeForce 1070/1070TI/1660TI/3060 for pocket change if you're fast. Also I5 Skylake/Kaby Lakes with 800/900 series GeForce PC are somewhat easy to find and there seems to be a number of I7 6700K and 7700K processors sold separately. This would be 150-200€ the cheapest, with one PC worth of electronic trash (or to browse the internet).

Well, this was the best I could come up with. What would people recommend with similar performance with the performance above? Or something I should take into account? I'm also interested in memory speeds and such, as I would prefer the better option - for example the difference in performance between 6700K and 7700K is small, but what makes 7700K actually a more interesting option is that 7700K supports faster RAM speeds.

I've been focusing more on Intel/NVIDIA, because AMD is much more rare to find. AM4 socket would be interesting because of how many generations it was used, but most older systems with AMD CPU are AM3 or older socket. 

I'm a bit surprised you can't find any AM4 CPUs, considering how many upgraded to Zen 3 over the years. I was expecting the CPUs to be plenty by now, just the boards being rare since you don't need a new one to upgrade your CPU.

Have you thought about refurbished MiniPCs? While the GPU won't be able to keep up with an used 1070 or 3060 (surprised you can find the latter so easily tbh), you can get one with a Ryzen 5 2500U (8 Vega CU GPU), 16GB RAM and 512GB SSD for less than 200€. And if a Celeron would suffice, you can easily go below 150€, though the GPU will be much weaker in those cases.

I checked out the mini PCs, it seems that required specs with the budget isn't available. The minimum requirement for GPU is GeForce 1060 6GB and If I understood correctly, the Vega is integrated GPU that doesn't come even close. 

RTX 3060 seems to pop out every now and then with old systems, but cheap ones are sold quickly. It was the budget option 4 years ago, so it's possible they've been used in Bitcoin mining.

AM4 processors are available, but the motherboards are not. It looks like that at my budget range, it's maybe 1 or 2 AM4 motherboards and 10 Intel equalents. Buying a semi-obsolete gaming PC with usable motherboard or graphics card hives you a decent case and a power supply. And if I decide to upgrade the system, there's something I still can use.

I bought a gaming PC for my second kid over 1,5 years ago. It has I5 11400 processor and 3060ti GPU, sonit's possible that someday either the motherboard or graphics card ends up to the PC I'm currently planning on building.

150€ isn't a lot of money and, if you can get a 7700K and a 3060 for that much, I doubt you'll find something better. With that said, I don't know much about the used market, much less the one over there.

Have you looked for used Steam Decks? It may be another option and can be used like a regular PC. but I don't know if the games you've mentioned run well on it.

It seems used Steam decks are over my budget. Apparently there's some issues with controls on Cottage Simulator with Steam deck that the devs have said they'll fix. 

3060 and 7700K is more or than and. And even then it's the high end of the budget anyway. Either you get better graphics card with crappier CPU or better CPU with crappier GPU.

I just offered 50€ for a 1070 graphics card and 80€ for a PC with I5 6400, GTX 960, 240GB SSD, 16GB RAM and 750W PSU. If I get the computer, I try to bargain a nearby I7 6700K processor to 30€. If I get all of them, it may be close to 200€. If not, I have other systems in mind, they're just not as close to me as these are.

As a reference point I still own and operate the i7-6700k and it will get you by for most games, save for some of the AAA games in recent yrs and some of the latest sim-based ones (as those require more cores and juice). 

If you could somehow get a 1080, you'd be kosher for a while, though I would personally hold out for a 1080ti by some miracle, since that GPU has gotten me by this long, even at 1440p. 

Well, as someone that has been using a 1070 for the last 8 years, I can tell you that it's a great card and will likely do very well with those two games. It doesn't really have a lot more life into it, and new big budget games will run like crap if at all (no ray tracing hardware), but for smaller or indie games, it's still an ok card.

Yeah, ray tracing is in RTX cards (and GTX1660TI). 2060 would be better option than 1070 and 1070TI, but they are nowhere to be found with the budget I have. All 2060s I've seen have been in +300€ systems, with no standalone cards that I've seen.

The more you're planning on building your own PC, the more evident it becomes how undrrpowered harware consoles are, though you get what you pay for, and how easy it is to shell out 400€ and be sure every game released for the next five years will run on it as intented. 

I was actually surprised how well 6700K and 7700K hold against even the latest base I5 processors. This, however, could be because of the code that may not use all the threads in newer processors.

1080TI would be cool, although a bit too expensive at the moment. Performance wise it's close to 3060TI. This system may be updated with 3060TI at a later date if I upgrade my second oldest kid's PC's graphics card some day. Maybe 4070 (or higher) a year from now when they're a bit cheaper. 

A Radeon RX480 or RX 580 (Or even the 470 and 570) would be fine... Or even the Radeon RX 6600.

Any Quad-core or better CPU made within the last decade... And of course make sure you have a decent amount of DRAM.

If you are on a budget, you need to ignore nVidia.