Well, the Kingdoms line had battle packs (which are now ridiculously overpriced on Bricklink), and the new Castle line has a nice little set with 4 figs and enough useful parts to make it useful for more than just the figs.
I hope this one will max out at 13 euros, but it's probably going to be 15-16, at least I fear it will.
SW has a lot of battle packs but because of the license they are still pretty steep - 17 euros for a pack with 4 minifigs here.
If you want just the figs, I built a lot my armies by buying minifig parts separately... If you make units in large enough amounts and you take some time to figure out the best offer (the fewer orders you need to place to get there, the fewer shipment costs you'll have to pay) I think this can definitely turn out to be cheaper than buying full figs / sets.
Most figs are expensive, but sometimes you can also find figs from random old themes really cheap... I just got 7 Blacktrons for and 6 M-Trons for less than 1.50 euros each. Putting together some of Warhead's Terrorkhan made me realize just how cheap these guys were, and they look cool, too.
If you want to save some money, you could by blank torsos (generally they're cheaper) and custom decal them. It works for me and also helps to give your army that 'unique' feel:
The bottom line is to plan ahead and to start out by buying the things you need the most of at the cheapest price, while avoiding having to place one order to get 1 part you need. The more fancy stuff like epaulettes and capes you want, of course, the more expensive it's gonna be. You don't need to have a huge army to have a good fight though.