I use some 6XAA battery packs to make 9V cells for my Quickie.
The batteries I was using were $10 CDN for 48. This worked out to two batches of batteries. They took forever to die... so long that I had used most of the second batch by then on all the other projects around the house
The D cells seem to have a decent amount of life on them and have never strayed from the name brand cells.
All that said, I am considering some rechargeable batteries for an off grid system I would like to complete... I look forward to seeing what's suggested as I plan on having an amplifier on batteries as well.