If your house is at 70 then you don't need a heater. If you pick the right low tech plants an inert substrate works fine (play sand, pool sand, colored gravel, etc). It will be fine for plants, snails, and shrimps. Plantwise I would stick to mosses, java ferns, and maybe floating plants.
Petco will ave similar low cost startup kits. Or check craigslist, you can get great deals there. I recently got a 30 gallon, a stand, heater, a gravel cleaning hose attachment, and 2 air pumps for $40.
A heater is better, of course, but since we are going low cost here it is the first thing I would cut.