this is indeed a fantastic idea. i agree the different models (cheap-0 tab and a nicely possibly bound full score) would be helpful- some people really just want the tab to try and play it, and some non-musicians (and musicians) would definitely be into the collectible aspect of the full bound score. really, you should get paid for the time it takes to transcribe; i (moreso than greg i'm sure) am ultra slow at it. so putting them online for free would sort of be shooting yourselves in the foot. this is a great way to make something back from the time it took to create and transcribe what you guys do best- the music- rather than just whip out some multi-colored long sleeves and sell them at $35 to try and make a buck.
i agree with avi that this is a great, unique merch item, and the more individual or artistic you can make it the better.
at one time, an artist friend was thinking of creating individual covers for demos to give to people. it may be more daunting for the level of interest you guys will probably have, but if the price needs to be higher to cover it, i bet many would still go for it ($40-50 is not out of sorts if it's really cool and has neat0 notes and stuff- especially when you consider some people pay $25 for a t-shirt).
also, this is especially good for your music, as i highly doubt many people would be interested in a full score of (insert joe average death metal band name here).