active mini-dp ---> dvi adapters cost $30 on newegg if you are worried about having to spend $100 on an adapter. Do NOT spend $100 on an active display adapter! They can be had for much cheaper.
Can sli run 3 monitors using dvi? Yes, the newer cards can. 4 monitors is not supported, unless you run them non-sli.
I thought active dvi to dp converters are only able to run eyefinity