Selection is always going to be limited at off-airport locations. You could get lucky, but MCO has one of the largest selections in the country given how large it is, and with Alamo, especially so.
What you can do is to book both off-airport and MCO and see what they can offer you at the Four Points/International drive Alamo, and if you're not happy with that, you can always just tell them to cancel it and head to MCO instead.
You might also want to use the link below to request a quote. We have often have excellent prepaid deals, and the differential between Alamo and National may be much smaller than you've seen elsewhere.