Well, the '66 Regular Carbine is a great gun. While the newer model Remingtons seem to be improving, the jury's still out on them. They've had some issues. There's no question that the quality of workmanship and material is better on the older models. I, personally, would pay more for an older Marlin than a new Remlin. The deer carving models were true Marlins marketed to stores like Sears, Speigels, Wards, etc. They are fine guns and, given that there were far fewer manufactured, have a certain collectable value.
The only thing about a used gun is that it may have a problem that you may not be aware of (and there's no warranty). If it was misused, or left to rust, it could be a problem. If you are familiar with guns, check it out thoroughly. Look at the action, remove the bolt and check the bore, and look at the ejector. The amount of wear on the ejector is an easy view of how much the gun was used. If you're not comfortable doing this, take along someone who is (or check out Youtube clips on field stripping). In most cases, 30-30s were bought for deer hunting and shot infrequently. Rarely do they have significant problems. And if it does have a problem, you can usually get it easily fixed with advice from this site.
If it's in good shape, $300 would be a good price. If it's in really good shape, you could go up to $350. The value of the scope is marginal, unless you are planning on using the gun with that scope. In that case you could go up another $25.
And keep in mind that this is only my opinion, and I have not even seen a picture of the gun. You are wise to ask, and listen carefully to what others here have to say.
And welcome to MarlinOwners! - this is a great place full of friendly and knowledgeable folks.