No way you can move the WiFi card to a different slot to give you more room? Another option is a cheap USB WiFi dongle. If you didn't have to limit yourself like this you could get a much better GPU like a GTX 960 or R9 380 in your budget.
Also keep in mind than when a GPU says it takes 2 slots that doesn't mean it plugs into 2 PCI slots. It still only plugs into 1 slot. It is just the width of 2 slots and it will block 2 of the openings on your case.
um, what mobo do you have? usually the first two slot positions are driven by the CPU and are ideal for a graphics card. the further slots are driven by the chipset and are best for storage and wifi adapters.