I started out with GTX 260 (40-60 MHPS) and a GTX 560 (100-150 MHPS). From reading these forums for about a month or so, I realized the Nvidia cards were terrible for mining but I wanted to get an idea of Bitcoin mining before I bought an ATI. I was mining with these GTX cards when BTC was trading at $2 USD (LOL!) and losing about a dollar a day or so.
It doesn't work that way buddy. If you purchased a half-decent mining card as soon as you realized the mistake you had made, you would not have been pouring money down the drain in the first place.
Once I got a hang for the software, pools, hardware, etc with the Nvidia cards, I went out and bought ATI.
That makes it sound as if mining with AMD cards is somehow magically harder than with nVidia cards... that's the costly approach again, you needed to switch ASAP.
The only piece of advice I can give the OP is, grab some AMD cards ASAP and when they arrive sell your nVidias to recover some funds quickly.