Check out page 75 here.

I'm surprised - some of Infiniti's recent models have instructions that start out with "remove front bumper" so apparently the M is engineered to be a little more maintenence friendly in this regard. The process does not look difficult at all.

The cost of the bulb itself is a good portion of what you've been quoted. You can typically find replacements in the aftermarket much cheaper. You will need either a D2S (if you have projector style lights - I think you do but confirm this) or a D2R for reflector style.

For the bulbs to match you will need to replace both sides with a matching set. As the bulbs age their color tends to shift, so even if you buy a new factory bulb, it won't match your 4 year old bulb on the other side. The factory color is probably somewhere around 4500K. The higher you go the more you will get a blue or even purple hue, and less usable light.

Good luck!

Heath