check out walking shoes with Vibram soles.
from the likes of Mountain warehouse.
If using dedicated cycling shoes with the
option of using cleats and you never intend to use cleats, I'd glue down any cleat cover or at least make sure that it is firmly screwed down - sometimes the cover detaches.
Also worth keeping an eye out for Lidl and Aldi specials on walking shoes or cycling shoes - sometimes they do good firm soled shoes for under £20.
Also worth keeping a look out on
ebay for vibram soled shoes second-hand.
I recently got a pair of shimano thingies, "used" but clearly not worn, for £20.