I've been able to find military mags for around $30 at gunshows here in South Florida. Factory mags run around $45. That's as cheap as factory hicaps get! Stay away from USA in the future. Some of their mags work fine, but many don't - it's not worth the risk/hassle. If you can't find factory/military mags anywhere (check Shotgun News) then Promag seems to be the best aftermarket mag manufacturer. But it really is better/smarter/cheaper-in-the-long-run to spend more money and get good mags.
JMHO and HTH!