under the 15yr rule you can import cars with mods no probs and generally are worth it if you can find a nice example. There was this sweet R32 GTR with an almost brand new N1 engine fitted (yes the red one) for around $25,000... now that was a nice R32. I suggest you stay away from the dirt cheap examples with your budget, some look like they've had a hard life.
Getting one under SEVS isnt worth it in my opinion, you'll pay bucketload more for compliance for a car thats only a couple of years younger.