Current value is what you need to be aiming at in any event. I think that this is some sort of variation on the ol' capital gains, although I doubt that the IRS will be worrying about this too much.
(When my friend was set to donate his old bassoon to a Lutheran secondary school, I bought it from him instead for the value of the tax donation (and made out the check for the full $333.33 allowed (and would have continued the repeating decimal out if allowed for in US commerce).)
And, yes, Bundy branded contra-altos (which are really basses, but let's not quibble) have been produced for many many years. Most that I have seen and used are beaten to death, and you can occasionally find them in school district auctions for a bargain price (which is probably along the reasoning you are following in making the donation in the first place.