Given your foot pain and desire to get a road bike, I would advise you to get some decent enough road or mountain shoes for the spin classes that are on sale and not top of the line. A fiberglass/plastic sole will be just fine for spinning. Stiff enough for that yet cheap, and it'd be easier to find a road shoe with the 2 bold SPD pattern. (I'm assuming that you're using those double sided pedals and it's not a place where you can bring in your own pedals). These shoes could easily cost less than your running shoes and will last forever for spin workouts.

Then when you get a road bike, get a nice pair of road shoes that are a bit stiffer (carbon if you can afford it and don't have any foot problems that would make carbon bad for you like a nerve problem, etc.). With these shoes, get a wide platform road pedal system like SPD-SL, Look, Speedplay, etc. This will probably give you the better comfort and performance you will be looking for with your road bike.

This is what I did, and it has worked out great for me. When I was budgeting for the road bike, I took things like shoes into account. My spin shoes were cheap and about 2 years old by that time (I was also a student putting off the big road bike purchase). They are still going strong as spin shoes, but I am very happy to use a different pedal system on my road bike.