I just booked a one way from MCO to RSW. I got the best rate by booking a week in MCO with Dollar ($234) and then 3 days MCO to RSW ($122). I tried to get one to price match the other, but no luck. I used Zalyn.com and signed up and they keep track of my discounts and apply them. The bookings have mostly been on Priceline (no credit card) and I have been able to cancel at no cost when a cheaper rental has come up.

Someone posted yesterday or the day before on this forum about getting 100 credits from Zalyn towards automated searches by using the promo code FLYERTALK -- it's explained how in the post.