I don't know how much cheaper the Costco rates are for you, but it was cheaper for us to get a regular membership ($55) and use the codes. This is our second rental car with this membership, and it paid for itself in the first use!
On another note, I personally would be ok with Budget. We were the same way till we had a rental with them out of MCO. They were awesome and the customer service was so much better than we had experienced with Alamo. When we were getting our car, I asked what we were getting. The guy checking us in told us and then asked if we wanted something different. I said, I don't know what else do you have. He rattled them all off and said pick whatever one you want, and if you see it and don't like it, come back and we can change it to something else. I was impressed with it.
We also had an issue with Alamo about the tolls (we paid cash, they said we missed one so was charging us an extra $60). It took several calls over several weeks to get it fixed. With Budget, they have a sun pass in them that has a switch you can flip off. We didn't realize this so ended up using it by mistake (it reads it and automatically paid it). When went to return it, the guy said he couldn't take it off, but he could go in and reduce our cost the price we would have been charged for using the sun pass. Amazing.
We will rent from Alamo again, but have no doubts about renting from Budget.