You could always do a pot roast that easy enough, and very traditional. You could put some ribs in the crockpot with BBQ sauce and either apple sauce, grape jelly or apple jelly. The ribs turn out wonderful! Another very inexpensive option would be a pork shoulder you can usually get them on sale and are very inexpensive and will feed a LOT of people with tons of left overs. Here is a good recipe for that:
http://www.msnbc.msn.com/id/30890488/ns/today-today_food_...
Kroger is always running specials on a complete dinner meal. I think this weeks was if you bought a ready to eat meal (like the kind you microwave) you get a 2LTR of coke, a side, salad and rolls for free. You would just have to check their ad.
There are tons of soups and stews that you can make. They also make crockpot meals in the freezer section of the grocery store. Everything that you need is in the bag, just throw the ingredients in and your are done =) Since you are cooking all of these crockpot meals I would HIGHLY recommend the crockpot liners they save so much clean up time... Love them!
Good luck and hope this helps.