Beware, the CZ 527 mags are already scarce as hens teeth and very expensive.
You can buy all the 5 round mags you want right now on eBay (probably GunBroker too) but you are very right about the cost. Most are $50+ by the time they get to you.
The 223 are available and around $50, but the 7.62x39/ 6.5 Grendel/ 6mm ARC are over $100 apiece and hard to find.
