Well, i wouldnt say they are cheap...

One local shop sels them 12.5 Euros each (that would be around 16 $ i think).
But i'm not planning to by them today so i can spare some money for that.
Maybe i could by eight of them first and maybe eight more later? My tank is also quite well filtered (1 Eheim 2028 external filter and 1 New Line internal filter, wich regain 500 l/h) i do water changes once per week or bit often sometimes.
So maybe i could keep those tetras with sid's also? Least as long there is many inough to call them shoal. Maybe later i will replace them with some other shoal wich have the same region with sid's
Here is a bit old picture of my tank:
http://kuvablogi.com/nayta/252548/. I have done some small chances since that was taken, but you see the idea. Is there something i should change so sid's would get on well in there?