I agree with the others, they are well worth the cost.
Regarding your sources - think outside the box. Check local restaurant supply stores, they should have the durable, good quality mats.
Another thought: we replaced damaged carpet in our family room about 10 years ago. We had paid for the mid-grade pad, but the installer only had the top-grade on the truck, so he installed that at no extra charge. I have plantar faciitis, and I will tell you when it flares up, that pad makes a HUGE difference. I can actually walk barefoot pain-free in that room only, whereas the rest of the house I have to wear my ugly crocs or other soft, squishy footwear. Might be worth checking to see if you could purchase a remnant or section of the high-grade carpet pad.