Go on the National website, play around with your dates & various codes...you'll be surprised at how much your rate can vary! As always, check out MouseSavers.Com for hints/tips/codes - but it looks like you've already done *that* since you know about the Priceless code & Entertainment coupon...
*Sometimes* it has actually been cheaper for me to get a towncar to WDW & then pick up my National rental (after my vacation has started) from the Magic Kingdom Car Care Center, rather than renting a car at MCO for my whole vacation.
If you do decide to do this, one thing to be aware of(but not really a problem), is that the MKCC doesn't technically have an Emerald Aisle, but they *do* have Emerald Counter. There's only ever been a person or two in line when we've rented from the MKCC, though. Last time we used the Orlando Airport Emerald Aisle?...it took about 15/20 minutes to get out of the parking garage. The line of waiting cars was unbelieveable!
agnes!