Don't bother. Any turn table that can play your records can be connected to a USB audio interface and input to a computer. Most USB turntables I've seen are pretty low quality. Buy a "real" turn table and use the Mac's built-in mic-in jack if you must. Yes you do need to apply RIAA decompression but you can do that in software Audicity is free and get do that.
If you have a record colect them maybe even you have a turn table already.
But I agree that if you can afford it get a nice analog turntable and sound recorder or run it into your mac line in. Arguably a good turntable can provide sound that is on par or surpasses CD sound quality if done right.