Hi,
Hard to be too specific, but I would think that given the time needed to strip the paint,drill out all the old bushes, clean up the boiler shell, make new bushes from Bronze, Silver Braze them all into position, clean up the flux residue and retest the boiler to 2 x working pressure then repaint, I do not think you would get much change from $100 - $150.00... there is quite a lot of work involved... a good 3-4hrs + paint drying time... it would largely be determined by how many bushes required replacement... if it were mine, I would replace the lot and be done with it.
I hope this helps.
SandyC.