When it comes to printing your headshots, using a professional printer service is just as important as your photographer.
You need to factor this into the investment in your headshots. If you take your pro photos to your every day print lab, the images will most likely look horrible to casting.
Take the printing of your pictures seriously - do what you can afford, when you can afford it. If you can only have 1 or 2 shots printed well, that's much better for everyone. You can work with those and then get some more printed when you afford more.
Please don't settle for printing at FedEx Kinko's - agents, casting directors and managers will always notice and prefer a professionally printed headshot.