I have 4, no 5, of them.
So yeah I like these cameras, they are sensibly light and compact, focus nicely, and can have exceptional optics. (Ricoh Diacord, Minolta Autocord, Yashica Mat 124G, Yashica Mat 44, and a pre-war Zeiss Ikoflex)
Here's an overview:
WWW.TLR-CAMERAS.COM/TLR Categories
Cheap? The Ricoh Diacord, or other Ricoh or older Yashica models.
Reasonable? Minolta Autocord; Rolleicord, Yashica Mat 124 and the like
Expensive? the 2.8 Rolleiflexes
These are all fixed lens models. A good Autocord is butter smooth and has a great lens. Rolleis are also butter smooth, excellent construction, but you pay for the name. The Yashica Mat 124 (I have a 124G) has a built in meter, but the lens isn't usually quite up to Minolta/Rollei level. The Diacord is inexpensively built, doesn't have auto shutter cocking, but puts its value where it counts: the lens is very very good. The other Ricoh models, and older Yashicas, are all decent performers, though I don't have any experience with them.
Really, you can't go wrong with any of these... and some of the models have built in light meters, which you may want.
Then there's the series of Mamiya C's - C2, C3, C22, C33, C220, C330 - which are bulkier than the fixed lens TLRs but have interchangeable lenses. Again, with the later ones, you can't go wrong if you want the lens-change ability.
Some Yashicas, Richos and Rolleis had 35mm adapters - I'm not sure, but there may be more. These can be difficult to find, and/or expensive... and I'm not sure how useful they really are.
I've only scratched the surface - there are Meopta/Flexaret devotees, Ikoflexians, Ciroflex/Graflex-22'ians, and so on.
A beginner model? Really anything at all goes! But to get the fun of the experience, something with a crank wind that also sets the shutter is easy, cool and simple. If you're worried about having a light meter, get one that has it (I bought the 124G with the thought that my daughter would use it), but you can get by with a hand meter just fine.
You'll need a lens hood; most but not all have standard bayonet fittings, i.e. a Bay-1 will fit many f/3.5 lens TLRs. Due to the geometry of the thing the lenses tend to flare.
Personally, I started with the Diacord, and loved it. Then came the Yashica Mat, then the vintage Ikoflex, then the 127 film 44, and finally the Autocord, which I actually got CLA'd and have new leather for. The Autocord is my favorite.