They're just under $1.50 each if bought 10 at a time here:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
When I first started playing here, I relied on them. Was far less likely to reach the goal with a regular cover so I tried these. Many providers are friendly towards them, though may or may not have tried them. They are much stronger than regular covers and feels like going bare for the guys. You can put one in in the front of the encounter and still DATY and play while it's in there as the outside is easily moved out of the way. Its internal positioning is not likely to move much due to a kinduv stiff ring that keeps it in place inside her. I always keep a couple with me - just in case...but now use an imported male cover that is so thin, it's damn near the feeling of bareback, too. These things:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
But if you're too well endowed they're really hard to get on. Non-latex, too.