Costco is somewhere around $50 or $60 to join these days. Personally, I think its well worth it even without the car rental discount, but thats another subject for another board.
What I would do is go into Alamo's site, click the 'More Options' link, then your locations and dates, then enter 7014627 in the I.D./Corp Id field and AD8221SDF in the Coupon Code field and see what you get and compare it to your Hotwire numbers. Also note that when you look at the details, 1 additional driver is included.
Now, I will say that I've used Costco codes with Alamo IN ORLANDO (and a few other places) and have never been asked to produce my Costco membership. However, I've always been prepared to do so.
I'm also not trying to imply that the Costco discount is the only one that has the additional driver, nor am I trying to imply that Alamo is the only one that sometimes includes the additional driver. I would encourage you to look around for discounts with other rental companies and see what kinds of deals they have going on. I see you're going in March...if very early March, you may have already missed the discount windows, but for mid to late March, prices (again for MCO) appear to be dropping.
When you do look at other companies, use the companies website, not aggregators like orbitz, expedia, kayak and the like. They show basic rates, but generally don't find specials.
Finally, and importantly, when you find something, book it, but don't prepay. This gives you the option to switch to something else. Rates can often change daily, or even multiple times in one day, so if you're not prepaid, you can look right up to when you leave.
