i think 300 us dollars.
Sounding reasonable, so far...
but i want a ppc.
This is stretching the budget, but not impossible, with the A1200. The PPC accelerators are a lot cheaper for 1200 than for an A4000. You'll probably need an upgraded power supply and some other bits and pieces, though, as well... I'd guess you've already busted over your budget.
a voodo card
This is meaning you need a tower case, upgraded power supply, and a Mediator. The system by this point is probably going to at least double your $300 budget....
i dont kown if i can get a complete good amiga in ebay for better price
Probably... The complete systems sell for quite a bit cheaper than their parts. You're still not going to find an Amiga of the spec you're looking for at the $300 range... Probably more in the $500-$700 range.
Everyone uses commodity hard drives and RAM. They are the cheap and easy parts of the system. It's the PPC accelerator and PCI bus that are going to cost you.
The Amiga hardware is older... But it's rare, and still in demand by both users and collectors. It's held it's value incredibly well. Really an oddity in the computer world.