$75 per door is too much. I asked two locksmiths in the New Haven, CT, area (not a low-budget location) and both said $20 per cylinder.
Here's the deal. Your XJ has two different keyways, A3 and A4. One is ignition, one os doors. Despite the difference, the ignition key will fit the door cylinders, but the door key won't fit the ignition. The locksmiths said as long as the ignition key fits into the door locks, they can rekey the door cylinders to work with the ignition key.
Don't forget that the hatch uses the same key as the doors, so that should be rekeyed also.
Start by confirming that your ignition key will go into your door locks. It does on both my 88 XJ and my 88 MJ.
Find the best ignition key you can, preferably an original. Copies lose a bit of accuracy every time, so the 'smith will do better with an original key (unless it's all worn down, in which case it doesn't matter if it's original or a copy).