I found Kester 44 63/37 Rosin Core 24-6337-0018 at Stanley Supply Services for $21.28. With shipping is was $28.45. This is the cheapest place I could find Kester Solder. The diameter I went with was 0.025, but they have 0.031 at $20.85. I am not affiliated with Stanley Supply Services in any way, just been looking for the cheapest place to find Kester solder. I should get the order in by the end of the week, and I'll update this thread about the packaging etc. Let me know in the comments if you find Kester 44 cheaper at another store.