No kidding! Esp. since it didn't work!

I think if you find 10mg works for you (2 of the 5mg) at the same time dosing... getting an RX for 10mg may be less expensive than taking 2 of the 5.

CII controlled drugs are more expensive than others because of all the paperwork and hassle in making, shipping and storing them. The raw material of the drug is even rationed yearly by the DEA. At the pharmacy level, there is a lot of time consuming record keeping of the invoices, order forms, and dispensing logs which is not done for non controlled drugs. This all raises the price.

Also this particular drug is less used than say, Adderall, so it will be more expensive. You might like to ask your pharmacist for some price quotes for generic Adderall and see if they are less (if you decide to continue with amphetamine at all).
Adderall is a mixture of 3 types of amphetamine which lasts longer in the body. It is actually the preferred form these days. Dexedrine is an OLD product and contains only dextroamphetamine.