I would check with your local Safekids and see if they have any program seats available. If you qualify for WIC, you may be able to get one through there as well. The Health department might have ideas as well.
Otherwise, I would recommend you look at the cosco scenera next if your 2 year old is smaller than 40 lbs and 40 inches and still rearfacing. It costs $40-45 at Walmart. It rearfaces to 40 lbs and 40 inches and gets most kids to about age 3 in it. Hopefully you could save up enough before you absolutely need a seat. If your child is close to 40 lbs and 40 inches and forward facing, I would recommend looking at the Cosco Finale, which is also about $40-45 at Walmart. It forward faces to 65 lbs. Again, hopefully you'll be able to save up enough in time if safe kids or WIC or the health department can't help.