I agree about Mordhiem. The rules are free to download from GW Specialists Games *gasp*, and fielding a warband is dirt cheap, even going the GW route. Want to play Skaven? All you will ever really need is a single box of Night Runners from a discount retailer. If you absolutely must have a Rat Ogre, buy it dirt cheap from someone selling the contents of a WHFB boxed set. For most of my forces though, I just bought random figure lots on eBay for next to nothing, which fits with the spirit of the game perfectly. My dwarven artillery crew figures, for example, are dead-on perfect for this game. Any ol' miniatures will do, really.
Alternately, with a little conversion work, a single Perry Miniatures "Mercenaries" boxed set gives you enough figures to field 3 whole mercenary warbands. Alternately, mixing and matching pieces from a few Wargames Factory boxed sets is an affordable way to get an entire gaming group started (3 box sets is enough for 6 players). That's probably the route I will go when I start up a league for the kids who get dumped off after school at our local library (cheap enough to let them keep the figs even if they keep at it).
Most of all though, the game design and aesthetics really harken back to the golden age of GW. I've taken a lot of joy in the conversion work that I've been doing for my warbands. A lot of the the terrain that people make for it is absolutely inspired.