Well around £30/$40 for the retail games, a few will probably come striaght out at the £20/$30 mark as on the PS3 and the store will cover the rest quite easily, I myself have bought around 60 titles off the store for the PS3 in the last 12 months lol
And the Vita I imagine will be compatible with all of these titles, along with a host of new titles designed specifically for the system, the store is our saviour yet again :)