rb20s are a very tough engine i tried and couldnt brake mine, so for up to 230-240rwkw with a 2530 or trust t51xx setup they are very goo and while lacking a little down low will rev to 8k all day. and cheap so if it breaks drop another in.
for 5k you should if spent carefull fit a cooler, turbo, exh, fuel pump, injectors and get it remapped to suit, for 5k you will be lucky to fit a std rb25 engine, so if 10 was the budget then its a diff story