You know I can only speak for myself.Usually a custom job is around $100 or so and includes a tuneup. (There are obvious exceptions to this)
Lenses, if you buy donors are $60ish. Rubbers - OK, I'll say $35, but a lot of folks have spares lying around.
There's extra value in a beater as people want to do customs, but don't want to ruin a good frame. A $250 beater XX would sell in a few minutes. A $300 beater would most likely sell in a few days. (Hence why I gave a "range" to my prices.)
Would you buy at $250? How about $275?
I have no Tune-Up Pro. in Germany to refinish the Frame.
So I have to send the frame to UK.
Same with lenses.
I have no extra Rubber laying around.
Only god know what els is wrong with it.
So no, the math is no good for me.