i wouldn;t have a problem with a 4 banger but mine is not lifted and i hardly get on the highway. i hear bad things about lifts, highways, and the 2.5.
i would imagine that for 4-6k, you could get a fairly nice wrangler. both of the ones the wife and i have bought were 4k or less and both were 6 cylinder, automatic, hard top, ac, full door jeeps. mine being an 87 laredo and hers being a 93 sahara.
I don't feel like working on anything at this time so i sold my yj.