I put the dates in Priceline, selecting cities locations instead of airport locations, and it gave several options at about 300CAD for 4 days. I went to Enterprise, put in those pairs and it accepted it. If you change the location, the rental was unavailable or price shot up to 1300. Not sure if it will be honored - maybe the local manager will refuse? Also, I tried Bellingham and Paine, and they seemed to be 1300 as well. Here's an example:

car rental price