The later Rolleicords are a good choice they are lighter than the Rolleiflex and do have a Xenar lens which is just as good as a Tessar. Earlier Rolleiflex are also an option but I don't always trust the Automatic film feeler. The Rolleicords are also usually quiet a bit less expensive than the Rolleiflex.
The Mamiya C330 or C220 are affordable and they have interchangeable lenses that are also affordable.
The Pentacon six has some great glass and is not expensive.
The Kiev 60 is less failure prone than the Pentacon six and has the same mount so great lenses.
The Mamiya RB67 can be found for under 600 Dollars and they are great just not that portable. Earlier Pentax 67 can also be found for under 600.
Basically it all depends on your shooting style rent (from friends, etc) a camera before you buy. TLRs are great just not everyones cup of tea the same applies to pretty much every camera.