Over the 6 or so years I've been into reps, I would have answered this question differently, depending on the circumstance.
At the start, I would have thought it sheer madness to spend more than $150 on a 'fake watch', but over time came to realise that some reps exceed the quality of some lower price gens (I had a gen TAG Formula 1 when I found this forum; it is now long gone) and then the pleasure I found in modding and Frankening made me re-evaluate yet again the sense in spending $3000+ on some gens.
As some before have said, I am more inclined to spend more on the models I really covet, such as the rarer, older models that you would never see in the wild, rep or gen. And the knowledge of watches, and the friends I have gained over the years of modding are well worth the inflated prices alone.
So, in answer to your question; straight out of the box from a dealer - $400-500 max. If I were to keep it, modify it and have it professionally serviced? $1000-2000ish. But you're kinda paying in instalments when it gets to that price range, as the fun for me is spending the time and effort finding just the right parts to make your rep that bit more special. It's a different feeling than just walking into an AD with a wallet full of cash and dropping it on the nicest gen you can afford. And in my opinion, worth more.