you could probably make the size work.

it doesnt sound like a screaming deal... but depending on the brand, its not bad. you can usually get full SLX frame's + fork + headset for around that much on eBay if you wait just a bit. though if you like the paint or it's a hard to find brand, $300 for a NOS frame is probably pretty good.

a fork for $50 sounds about right... the bikeworks NYC straight blade chrome fork is ~$57, spicer forks are around there too, though they are threadless.