I like the figure flats and I think Pinnacle's Deadlands line of miniatures look great. However, I want something solid and I suck at painting. Fortunately for me there are several Heroclix, Horroclix, and Mage Knight figures that would make great Deadlands minis. This is by no means a comprehensive list of all appropriate minis, but these are the ones that came to my mind.
The Bioshock Infinite Heroclix set has a great selection of minis that look great for Deadlands.
They have a nice mix of late 19th century/early 20th century garb with steampunk looking tech. You can buy the starter which has six of these figures for less that thirty dollars or pic up the blind single boosters. The Motorized Patriot gives me some great adventure ideas.
Need some tech? How about a tank mini to represent a secret USA or CSA project. The Mage Knight Dwarven Steam Behemoth Tank from 2001 would be a great miniature to use. You can get them relatively cheap on Ebay. I just snagged one for 11 dollars after shipping.
Need abominations, Horrorclix has you covered, especially the Freak Show Set. Boosters and singles are relatively cheap.
But you're asking, what about more cowpokes? Well Freak Show has a few that are appropriate, but The Jonah Hex quick force gives you three more.
There have been a few Jonah Hex clix. The newest is a tournament exclusive, and will probably cost more than you want to drop but the original Hex mini from Collateral Damage looks cool and can be found for less than six.