I use Beverage Control, Inc. off of Mountain Industrial. They refill or swap, I believe. My 5lb tank was under $15, as I recall, and may have been under $10. Only issue with them is their hours... weekdays, and I think they close around 3:00 or 3:30 or so.
I recently bought a 20 lb tank from them, so I am down to about 1 fill per year. Tank and fill cost less than my last tank did. Not as pretty, but...