Hi Karen ,have you checked out E bay ? There are usually lots of wetsuits of all sizes for sale on there, not just second hand ones but also dealers advertise new suits at all various price ranges.
If you are not sure of the size you need, if you see a suit you like and it's made by Mares for example, if you go to the official Mares website they will have a size chart that will indicate the measurements for each suit size. This is the same for all manufacturers
Failing that, if it's only being used once a year, there is always popping into your local dive shop and renting one, or even renting a suit out there ?