Buy used. I purchased a used neo-air all-season (predecessor to x-therm) off of gear swap a few years ago for $60. It’s slightly heavy at 19 oz and had a patch on it, but it has been very warm (much warmer than x-lite) and trouble free for me. I don’t see them on gear swap much – but you might start checking e-bay occasionally. I do see used x-therms all the time on gear swap.
Much of my high $ gear (packs, shelters, pad, sleeping bags, etc.) has been purchased used. If you have the patience to check various sources of used gear every couple of days over an extended period of time you can often find what you are looking for. I also jump on clearance of discontinued models when new models come out.