Is this the only place that has them?

http://www.renovatedradios.com/parts.html

Kind of expensive, I was hoping for something cheaper since the knobs are the only thing my set is missing.

Yes, as far as I know. I searched on ebay and one by one over months, I got a complete set. The channel and fine tuning are the most difficult. The two other knobs were also used in radios so not as rare.

Good luck.