There is a shuttle bus with Quick Shuttle, $41 pp Canada Place to Seatac. Can be dropped off downtown too. Since you are 140 miles away a limo would be costly, I recall, vaguely about a $300. trip?? there is also Amtrak, but I mostly drive, easy to pick up a downtown Vancouver car and drop off at Seatac. Handy with several layover hours if on a red eye flight.
I have easily found rentals in the $90-100 range, don't know where you are looking but I have rented from Avis, National, and Budget. I currently have a rental from Hertz for $90, of course if you are looking at a large car the rates will be higher, these were for a midsize.
Take Amtak! You can get a First Class ticket to Van Couver for only $18.00 per person. The trip is spectaculer! The train runs right along the water and the views are unbelievable. There is a ding car. First class plays a movie, but I have never watched it! The scenery is just to fantastic.
The rental itself was fine, less than mentioned. Thr DROP OFF charge for pickup in one location(SEA) and drop at the other(YVR) added on another $150.
Then, respectfully- you rented from the wrong company. I have NEVER had additional drop off charges and I would guess you went with Alamo??? As stated above, I have rented from Avis, National, Budget and currently have a rental with Hertz. I have never paid over $100/day.