I think that the idea about jars in a larger container of water is your best bet. Could you put up a card table or some other foldable table in a corner or along a wall to put a big container on with all the small jars?
As for the container, it doesn't have to be a tank, as MollyJean said, rubbermaid containers work great (about 10-15 dollars at walmart), or you could do a big rubber muck bucket (for horses, you can often find them at grocery stores advertised for laundry (I have horses, they're muck buckets... ;). It will be cheaper for you long-term to have one good larger heater that heats the "bath" water than separate heaters for all the jars.
Here are some links for containers: (big ones, so you can do lots of jars :)
This is great, nice and shallow for your short jars, but wide enough to put in lots
Here's a tub, this is just a site I found one at, they have them much cheaper at walmart and super kroger, but this shows you what it looks like:
I hope this helps, and please post pictures/let us know how it works for you, I'm curious now. :)