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If the drums are in good condition, the 250 is a very fair price. Wrap is not all there is to the drum, and should be taken as only a 1/4 indicator of condition. This guy selling you the set is a friend and you have a definite advantage in that he is willing to tell you all the issues. Replacing the tom mount should be with an original if at all possible. These are Yammies, and finding those will be difficult, but not impossible. Yamaha drums will hold the value as serious drums better than our funky love for the Pearl/Star stencils, as they are more of a curiosity for some of us. Not to say that these are less desirable, just easier to find, and the more rare the badge and wrap, the better we like them.
As far as the snare, those are sleepers. There are some very good Japanese snares out there. Star/TAMA had the KingBeat, Pearl the Jupiter, and Yamaha has that one, I think is an SD. And yes, they do sound very good. A Ludwig Supraphonic is, arguably, the #1 sought after snare for all playing situations. They sound great, but they are not the only great sounding snare. And then there are those rare gems that the Japanese snuck in here that can be had for a song, and they do sound every bit as good, and for WAY less that 400-500 bucks. I have a no-name Made In Japan chrome over steel that sounds like a supra. That drum alone could take you all the way to the top, without ever having to buy another snare. They are that good, no matter what anyone my tell you. There are people who will look down their noses at these drums, and I just smile, and grab them for 20 bucks, and they never know the difference until they actually see the drum. Good luck, and when you get some pix, post them up for us!