Just for reference (for each world that I've been to), here are the lowest and highest of the number needed to get to a 12500/1 ratio (or slightly higher in some cases because I always buy in increments of 10).
N. Midgard: 870 (seaside castle) to 2840 (blacksmith shop and pub)
S. Midgard: 900 (sawmill) to 1240 (inn)
Aegir's Sea: 910 (fortress) to 1240 (three different ones)
A's Passage: 980 (the last two) to 1080 (dry dock)
Vanaheim: all are 990, except the etin market (1010)
Nilfheim: all are 980 or 990
Jotunheim: two at 950, two at 960, one at 970
Alfheim: 900 (elf dwelling) to 950 (elf armory)
Nidavellir: 740 (dwarf mine) to 810 (dwarf blacksmith)
Muspell: 650 (fire fortress) to 700 (fire gate)
Helheim: 310 and 290
Vingolf: 290 and 280
Asgard: 280 and 270
Midgard GT: 220 and ???
I'm on the Facebook version, if that makes any difference...
Last edited: Dec 19, 2011