The CAI CETMEs are known to be 'hit or miss'. If you do buy one get it direct from Century so if you have any problems, you can send it back. I bought one from them and after a little tinkering, it runs great. Century buys these firearms, ships them to the US and detroys the receiver and barrel and rebuilds them using a mix of original and new 'made in the USA' parts.
If your into the CETME design,also take a look at the PTR-91 GI. These go for around $900.
As to the ammo question, best to stick with 7.62 NATO(READ LINK)
Don't be scared away from the CETME, just be prepared to tinker. I love mine
The Gun Zone -- .30 Caliber Ammo
Also, HK mags can be had in like new cond for .97 and many other parts are available.