The place I found with the best opinions was Alan's Wheelchairs (
http://www.alanswheelchairs.com/ ) They quoted me $95-$130 for an entire week. (The cheaper
ECV being a very lightweight model. They recommended the $130 heavyweight for park touring. They do have an even heavier-weight model @$200/week.)
They are located about 3 miles North of DL on Harbor Blvd. If you want the ECV delivered/PU'd at your hotel, they said there would be an extra $25 fee.