To me, best bang for the buck is slightly used tires that are in good condition. Go to a scrapper yard, and take your pick. The cars are there typically because of problems with the engine/body/etc but not because of tire problems. You should be able to tell a good tire from a bad one, though. Look at the date code on the sidewall. Don't buy tires that are more than 4 years old. Count on forking over $20-25 per tire.
I gather your Blazer is 4WD? For best life of the powertrain, take a flexible tape measure with you and choose tires that have the same circumference as the tires you still have on the car.