First off, can you get a few days inspection period to look it over inside and maybe take it to a range?
IBM made 346,500 out of 6,117,XXX carbines. About 5.6% of the carbine production. This example's serial number was about 1/3 of the way through their producton.
The receiver would need to be cleaned and checked. Heck, just the receiver could sell for $250-$300.
The mags and bayonet (and the bayonet can be cleaned up) will sell for about $100
The repo stock should fetch $80-$100 A GI average grade stock, maybe no cartouche would cost about the same, so a wash.
Rear leaf could be broken from vibration, $35-$40 replaces that. But might be ok to shoot as is.
A GI D clip sling and oiler runs about $45
One of my best shooters has a Blue Sky stamp. They are ugly, but do not always ruin the barrel.
So:
............. ....$600
................-$100 for sold parts
....................$0 stocks a wash
.................+$45 sling and oiler
And you have a shooter GI carbine for $545 that doesn't seem bad to me.
Gun shows around me sell beat up imports starting around $850. Us older guys remember the days. My first was $60 in 1976, and many between $100-$200 late 80's. Those days are gone.
Maybe not a good purchase as a first carbine until one gets some experience. But you could wait you whole life for some granny to sell one from her husband that has been sitting in her closet for less. And an original M1A1will run about $3500.