I dropped by the welding supply shop today and discovered 45% silver brazing rods are $22 per Troy ounce. Now I'm curious how much money I will have to spend on filler for the frame I'm hoping to build. Obviously the amount will depend on how well the tubes are mitered, which lugs you use, number of braze-ons, etc. I'm just looking for a rough estimate here, so any help would be appreciated!

Assuming this is your first frame?
You can get by pretty easily with 2ozs of 56%or 45%- that will give you plenty for the frame as well as a few practice joints. I'd recommend brass for the drops (if they are slotted), if you are set on using silver for everything, then you'd better get an oz of 50n for those.

Yes, this is my first frame. Thank you for the advice. I'll probably buy three ounces to account for my mistakes.

You might want to go to frameforum.net and search out Fred Parr. He sells filler materials and flux for a good price. Very helpful guy as well.