Many Repair Centers have SIM cards you can buy for around the same price. Your best bet is to try an Indirect (third-party) service center. They are more likely to carry them. Some even carry used SIM cards for $5-10.
You can also find them on eBay for $0.89-$5.00
What kind of phone do you have is it a nextel device or a sprint device. Unless it is a Sprint wolrd phne it does not have a sim card but a memory card. You can get them at any store that sells micro sd cards like walmart If it is a SIM card for a nextel Phone I would advise goint thru telesales as Tom said All SIMS are not the same