HP-15C (vintage) auction stats from that "famous" auction site, with data collected starting 9/8/2011:
No Reserve: 6 of 11 HP-15C's have sold. Avg. price: $156.40All calculators sold were in working condition. Various cosmetic conditions from average to near mint. Higher priced models sold with a manual included. Several auctions have lowered the "starting price" from what was first listed. No BIN sellers have lowered their prices (yet).
Start Price: 0 of 5 HP-15C's have sold. Avg. start price: $132.00
Buy It Now: 0 of 11 HP-15C's have sold. Avg. BIN price: $338.63
Edited: 13 Sept 2011, 8:15 a.m.