Egress window are just regular windows that meet certain requirements:
 Have a net clear openable area of 5.7 square feet;
(Or 5.0 s.f. for windows within 44" of exterior grade.)
 Have a net clear openable height dimension of 24";
 Have a net clear openable width dimension of 20";
 Have a finished sill height no higher than 44" above
the floor; and
 Be operable from the inside without special knowledge, tools or effort.

So "egress" per se does not imply any special cost. However, if you have a below-grade basement with concrete walls you would have to cut through the concrete to provide a space for the window and dig out a place for an outside window well.

In the southeast part of Michigan you will be looking at between $3,100 and $3,800.00.

Thank you both for the information concerning Egress windows. :-)