I'm not sure about the water table problem... in Canada, almost all houses have a basement, and most new houses are guaranteed for 50 years against water seeping into the basement, so they must have got the sealing worked out.
As regards cost, surely in England the builder has to dig down at least 4' (1.3 m) for the footings and foundations, so what's the problem in digging an extra few centimeters? Again, in Canada, most houses are raised off the ground a couple of feet (60cm) so the basement is about 3/4 below ground level, which allows for small windows in the basement.
Often, inexpensive new-build homes have the basement unfinished - that is, concrete floor and insulated walls, but no wallboard, and the ceiling is unfinished. The basement can be used as-is for the furnace, hot water tank, washer/dryer, storage, or as a kids playroom.
Or, of course, you can have someone finish the basement, or do it yourself.