MHG and ARP studs may not be necessary to hit 300whp, but is recommended for peace of mind. Hell, mine is stock with a MHG and ARPs...bought it that way. It's our most common upgrade for a reason...reason being that we will always be on a quest for more boost. You can easily get there with a ct26 upgrade, Lexus AFM + 550s and a boost controller, as long as your intake and exhaust is up to it. 3" both ways should do it. You'd probably be looking at an intercooler, hardpipes and some engine management to go much higher, though; I'm shooting for 400, and that's basically my entire shopping list. I may go with a cx racing t61 bolt-on, though.
That said, I'm with xzeror...1100 to 1300 sounds like a great price. 1500 would be acceptable, but with the oil leak and tag issues, I'd be surprised if he won't go lower.