Get yourself to a discount tire dealer where you won't get ripped off. The warranty on the tires you buy will determine how long the tires will last. If the front and rear tires are not a pretty good match, replace all four tires for little more than two.
Are your tires REALLY "Cracked" or is it just minor weather checking on the sidewalls? How old are they?
A good set of tires should last AT LEAST 5 years, or 50,000 miles. Have your tires checked by a competent mechanic.
If they are cracking they are past their use by date and should be replaced immediately to avoid a dangerous blow out
In January I had a minor accident with some ice and a curb. I busted my front tire and dented a rim when I skidded off the road. Luckily that was the only damage! I had to replace my two front tires and rim for a grand total of about 800 bucks. (Two tires cost 300 together plus a 300 rim plus about 200 labor [ripped off I know]). Anyway so at the time when I got the tires I had about 33 thousand miles on the car. Now I'm at 37 thousand. The new tires are fine. I'm noticing the rear tires (the old tires) are starting to crack a bit. The old tires have 37 thousand miles on them while the new tires have about 4 thousand. Should I get the rear one replaced as well? If not how much longer will I have?