I think many good, racing oriented machine shops are equipped to do the balancing and lightening along the way. They produce a report of what was done in terms of the weight values for each part including material removed from the crank. The machine work is certainly money well spent. Very low risk, high reward.
The catch, if there is one, is that you've got to get the crank out of the block in the first place. That's the tricky business as it requires a few simple tools, some heating, and technique. That's where the risk lies, cause you can F'up the whole motor if not prepared for the task.