We have 10 males, 3 in a divided 10g, 3 in a divided 10g, 2 in a divided 5g and 2 single 1.5g tetras (one is a continuing care tank, the other is for newbies).
I have 5 females in a 20g tank as well.
A lot of my tanks are second hand. Here's a break down of the cost of one of my divided tanks.
10g - $15
heater - $13
rocks - $3 (large bag)
plants - $10
caves - $30
filters - $15
So it's about $85 for me to have 3 males. The other 10g is the same deal, the 5g was cheaper and is not filtered so that one was $50.
I've spent about $4000 on my fish tanks though, so I know where to cut corners to pinch a few extra dollars and still give my fish everything they need. It was also spent over time, not all at once :)
We also give our fish about 3g of space except the newest betta and our forever sick boy, Kris :)