on average, how much would it cost to complete a whole buffalo nickel set consisting of average circulated coins?
They are pretty cheap to complete except for the 1885 and 1886. I think I paid a little over a $100.00 for the 1886 and $200.00 for the 1885. I chose coins that had a clear definition on the reverse, clear date and "Liberty" on the front.
The series can get pretty pricey, even in F to VF condition, I don't know the exact numbers but you can probably do a search on the bay, to get an idea. Here is one, http://www.ebay.com/itm/BUFFALO-NIC...299680?hash=item2cc1d19820:g:OSUAAOSw6YtZUp-E
At this point I think that dateless Buffalos heavily outnumber dated ones, so you could make the argument that "average circulated" means "no date". In that case, it could be pretty cheap.
I knew that and I still answered for Liberty Nickels (no clue why). I also have the Buffalo nickels. Hardest one I've had getting (only one missing) is the 1913-S Type 2 (runs around $300.00) for a decent one. I also do not have the 3-Legged yet. Otherwise, the cost was relatively cheap. I think my highest was $75.00 for the 1913-D Type 2. These all have clear mint marks, nice dates (not just readable), and good details. Good luck!