Can I ask, I'm just using a pair of trail shoes to ride just now. Can you actually use cycling shoes as they are without the clip in pedals ? Not really got the extra money just now and wonder if I just pick up a second hand pair of shoes to get me going.
Wiggle have entry level Shimano clipless mountain bike pedals for about £17-18, which is a good deal. Got my son a pair last year and they work just fine. Wiggle also have some pretty reasonably priced shoes too. My son has the dhb ones for about £32-33, and again, they are pretty good. A bit chunky maybe, but functionally excellent.
I use the same pedals on both my mountain bikes and my road bike (Time ATAC's) so that I don't have to fork out for two pairs of shoes. Pure roadies might have a fit when they see MTB pedals on a road bike, but it works for me.
You should be fine using most MTB type shoes with flat pedals, but if you can afford to shell out £17-18 for some entry level pedals, I think you'll really appreciate the difference they can make to your cycling.