Have you looked into using a knee walker instead of a wheelchair to keep him off that foot? Here's what they look like. You may be able to get a used one at better price. Don't know if insurance covers these but a few of my friends who have injured their ankles used them during recover to get around.

Here's what they look like:

http://www.amazon.com/Roll-A-Bout-Al...m/B001LJASQ0/2