Kapa - I have a couple of carbines, including an IBM, and I live in Parker. I won't claim to be an expert, but if you want a second set of eyes, let me know. I'd think $1300 would be a top-shelf price for an all correct IBM, but carbines are getting mighty hard to find and prices are climbing rapidly, so who knows. The CMP forums is a great place for info, but the CMP has been sold out of carbines for a long time, with no more expected.
That price may be out of line, or it may be reasonable. Kinda depends on the details of that individual rifle and the story behind it. And how badly you want one and how much you're willing to pay. If it's an all-original, as-issued, correct IBM with all IBM parts that never had any of the upgrades, field modifications, or arsenal rebuilds, and was smuggled home in a duffel bag, it may well be worth every penny. If it's a typical mixmaster that went through one or more arsenal rebuilds where parts were changed and upgrades made, then not so much.
I know I spotted what appeared to be an unmolested, all original carbine with as-issued parts and features and no upgrades, perhaps a duffel bag gun, at Green Mountain Guns once for sale on consignment. I can't remember what make it was, maybe Underwood, but it was priced right at $1000 and it was already gone when I hurried back the next day with the cash. This was 2-3 years ago.
Oh, and if you find an original wartime M1A1 paratrooper carbine with the folding stock, which would be an Inland, you'd better be prepared to sell a decent car in order to finance it! Those are highly sought after and command top dollar.