Get a "dirt" road bike: a road bike geometry and light weight frame with canti brakes and larger wheel clearance for up to 700x30 wheels. This bike is not made to withstand the sort of abuse a cyclocross bike would have, but it has the clearance for bigger wheels and canti brakes. This is a great setup if you don't plan to ride offroad/mud much, but do plan to ride on "dirty" roads and rough roads or a few firetrails or in the winter muck.
This formerly was the sort of bike you can find pretty easily in the 60s, 70s and early 80s, but suddenly it's either a "racing bike" that only fits up to 700x25 wheels (if that) or a cyclocross bike. If you have the funds a little more money can get Curtlo to build you such a bike.