Yes. This issue has been raised a number of times before. During one of the beta versions, the wages were lowered, but they were bumped up again and never revisted.

Fot that reason, I never bother to build a camp. But really, they aren't useful except as some early game meat shields, so no great loss.

But if you want to use them, I believe you can change their wages in the xml files.

I happened to be looking at the code last night and noticed that some time in the last few updates they had this added:

<WageOverride>0</WageOverride>

Which is presumably supposed to set their wages to zero.

So I guess it doesn't work if they still have wages.

They are fairly mediocre, I think they should enable the upgrade tag on hired units, myself.  That way they could maintain parity.

But yeah, the wages are outrageous.  I ended up destrying the camp, so I wouldn't have to fire those guys when they spawned, and then subsequently ignored the border towns. 

But if the specs for the mercs are such that they are not viable, then they should be revisited or taken out of the game.