IDEA: You could buy a cheap pair of mountain bike shorts with a liner of questionable quality and use it NOW, then later buy a quality bib-short and cut out the cheap liner on the shorts and use the outer shell of the shorts over the bib. (Or just the bibs on a hot day... if you don't feel too much like it is underwear.)

Make sure if you get any shorts that they have a full belt and not just a few straps on the sides to tighten things. If you don't have a full belt you will suffer from waist rollover.


EDIT: Some shorts have the liner attached all over top and bottom... that would be hard to cut out. But many shorts have a liner attached only on the top with a few small pieces of nylon.