I really like mine. A CMP Underwood marked version. It has had trouble with extraction since I got it. It's seen several smiths who didn't specialize in M1's but what I should do is pack it up and send it back to the CMP gunsmiths.
Ammo costs aren't really all that far off of 5.56/.223. One buys .30 carbine by the 50 round box, most 5.56 is sold by the 20 round box. One can find .30 carbine for aprox $14.00/50 and up online. Comparison to 5.56 per round cost is close depending on the quality of each. I've had good luck with the Keep shooting brand mags, 50/50 with the Korean mags, all my surplus mags are G2G. Spare parts are available.
A very enjoyable carbine to shoot and I suspect at the close ranges it was intended, very effective.