Wheel advice please

Right folks, now the nice weather seems to have arrived, i've ditched my winter bike back into the shed

BUT, i think i have found a use for it, i'm sick of doing the same circuits around here because thats what i've done for years and they are boring and full of hills, which i dont mind, but its a bit mind numbing going up and down the same places all the time

So it got me thinking, what about a cross bike, that way i can take advantage of the old railway line we have which goes for about 40 miles with the odd road section, but i dont want to take my normal bike down there because the risk of damage, So some advice on wheels for my winter bike would be great

I'm not looking to go spending loads of money on a set, infact the cheaper the better, even if they are only going to last through until winter again

What should i be looking for? it would be great if i could just whip off my wheels and put the others in, so 700's with a 9 speed shimano set, which i guess i can get separate