What is this Johnny Cash album valued at?

Well, my mom went to this one antique store and found a bunch of albums that didn't have tags on them. She asked the guy in the store what they cost, and he said if they didn't have tags on them, then she would give them for her for a dollar. My mom found this old Johnny Cash album that says "Johnny Cash sings The songs that made him famous" It says to be from Sun Records. So my mom went to go pay for the record and when the guy saw it, he said he didn't know how it got in the pile, mad at himself for saying what they cost, he still let her have it. We got home and we tried to see what it cost, we couldn't find it on websites like Amazon or E-bay, so that made us think about the value even more. It looks like it's from the 50's, but it's still in great condition. It says SLP 1235 on the cover under the sun records logo. If you could tell me, or even give me a website on what it's appraised at, it would be really helpful, Thanks!