I long since came to grips with this by establishing a personal "rep/gen ratio". Since reps like watches come in different levels of quality I vary it. For instance on original movement reps such as PAM 2893 PR and GMT or 7753 Daylight I am willing to go as high as 15% if I can get it to 95%. That percentage includes mods. So if the 2893's and 7753's regularly go at about $6,000 for gen I am theoretically willing to go up to about $900 including service/proper sealing, relume, Jimmy crown guard, new datewheel, Watchman cyclops (when appropriate), and Palp/Lello/Homer crown. In truth it is only the Power Reserve and 7753 Daylight where you can end up near that number. On the non-original movement but still high quality reps I max out around $350 and generally the ratio falls to 10% or less (other than cool reps like MBW's and or DW Daytona which can go as high as $500-600 including gen part mods). Finally, on the lower end no more than $120 and no mods.
Then again don't listen to me as I have way too much money into this "hobby". And the new trend in better VC's, AP's and IWC's isn't helping either.