You can get all of the quartets in an excellent set of performances by the Alban Berg Quartet on EMI for about $36 on Amazon and elsewhere. The Guarneri's first complete set (now on Brilliant Classics for $45). The late quartets only (quartetto italiano) are two 2-disc sets on Phillips for a total of $28. The Alexander String Quartet did an excellent series of the quartets on Arte Nova for $5.99 a disc--they've been discontinued but aren't hard to find. All of these recordings have very good to excellent sound. As you can see, it doesn't cost much more to get great versions of all 16 quartets than it does to buy just the late quartets.
Let me suggest an interesting alternative: If you look on Amazon for "Beethoven Complete Masterpieces," you will find a SIXTY-CD set that includes the Alexander Quartet's complete quartet cycle, the symphonies and concertos and Missa Solemnis (Bronfman, Tetzlaff, Zinman, Zurich Tonhalle), violin sonatas (Zukerman), cello sonatas (Bylsma), string trios and piano trios, all the piano sonatas, Fidelio (Masur), and other pieces. The entire set comes new in a box for $34-62, depending whom you buy it from on Amazon or elsewhere. Some of the performances are not so hot (especially among the piano sonatas), but much of the material is top-notch, often with excellent sound. The drawback is that there are no notes other than a CD with a PDF containing brief and generic info about the pieces. Overall, I found it a wonderful value, and IMO the Alexander String Quartet's cycle is in the top rank.