In reply to Greasy Prusiks:
Have you though of what you want it an pad? Taco or folding design? Thickness? Type of foam? Size? (both layed out and stored), nice (removable) shoulder straps? Metal of plastic buckles?
- Cheapest option; make (more) friends with people with pads.
- Second option; buy used.
- Third option: wait for a great deal
The decathlon simond mat is really cheap even without discount, but at 8cm thick rather thin and has plastic buckles. (not that heavy, so the buckles seems ok for the application). It is really compact and easy to carry, so if space is a concern a great secondary mat.
Don't forget; sometimes getting two cheaper pads can get you more total surface area to land on ( bonus points, if they can be joined), more flexibility and it's easier to stuff in a smaller car.