I've got a RC 6.8 that's currently for sale here on the forums:
http://www.rib.net/forum/f21/ribcraf...1-a-79425.html
It is a 2001 hull and has some cosmetic bits that need sorting (although it's away getting some work done this week actually) but it certainly is structurally sound with a sound engine.
As has already been mentioned you might be pushed to get a more modern 6.8 for the budget. The 6.4 (or 6.3 depending on when they were built) is not the same hull and on the narrower mould. It's not quite a good a sea boat in the rough, but is a fair bit lighter and that will save you some engine size or gain you some performance like for like so your budget might go further.
Both are reasonable to launch single handed if you know what you're doing, and both tow fairly easily although the 6.8 being wider is sometimes a tiny but more of a handful.