Many good answers here. I would just add that it depends on what you plan to do with it. Obviously a bike that old isn't going to do well on today's MX tracks even just riding for fun. The jumps are just too big for 28 year old suspension. If you are just going to fart around on it that RM would still be a lot of fun. It is also old enough that folks racing post vintage classes may be interested. I got offered $1000 for my 1977 YZ100 but didn't sell it. Vintage racing is pretty popular now. Good luck.