I got my XD500U on ebay for 80 bucks shipped if I recall correctly, and I have seen some even cheaper. It may be a little overkill for singing pumpkins, but any other smaller projector isn't going to be alot cheaper and you have the option to use it later for bigger projections. Planning on getting another one this year for singing pumpkins myself.
I completely forgot that AtmosFearFX had singing pumpkins.....I was thinking of going with the ones from the gentlemen that posts here that has the actual songs like Monster Mash, Thriller etc. Either way it should be a hit for the TOTs. I had planned to build a box around the projector if I did use it outside just in case of the weather....but u do have a point with a cheaper model. Something to think about.
Slightly off topic, but I just had to comment on the xd500u projector. I picked one up just before Halloween last year and ran the AtmosfearFX Ghostly Apparitions with it. One of the best Halloween purchases I have made. Planning on picking up another xd from ebay for this year to do the singing pumpkins projection.