The 5.11 / Blade-Tech Revolution holster is an inexpensive polymer holster made for a wide variety of handguns. It comes with attachments to use as a belt holster or as a paddle holster. I have one for a SIG P220 and one for a XD9 subcompact. I've used both of them for multiple day training classes with no problems. They retail for around $30, and occasionally LAPolicegear.com has them on clearance. I got one for my SIG P220 for 12 bucks.
I found them to be sturdy, comfortable, and easy to use. When you insert the gun it clicks audibly. It has good retention in the sense that I feel comfortable that the gun will not fall out even if I were to roll around on the ground. It doesn't have any kind of active retention like a Serpa or Safariland ALS, and it doesn't particularly conceal well. I think the best use for this holster would be for range training or open carry in situations where you're not worried about people grabbing your gun, e.g. if you carry at home around a farm or ranch or something.
Thumbs up if you need a holster fitting these parameters.