So, I just checked for grins on the price of a 105 gruppo. About $650.

http://www.probikekit.com/display.php?code=D0099

A Centaur gruppo. About $710.

http://www.probikekit.com/display.php?code=L0150

An Athena gruppo. About $890.

http://www.probikekit.com/display.php?code=L0048

I'm sure you could beat these prices, I know I have on the Campy Centaur gruppo by a mile.

Choices, choices.

Any of these I just mentioned would work well for entry level Cat 4 racing.

They are going to get mushed in the first crash anyway.

Back to the op, what custom builder are you considering?