2003 Chrysler Town and Country

Computer problem
2003 Chrysler Town and Country 6 cyl Two Wheel Drive Automatic 96000 miles

the engine light came on shortly after my daughter took the truck in for oil change, the mechanic said the evap system has a leak and wants to fix this but it will cost her approx. 375.00, my question is I never had a problem with this truck, first time someone else touched it other than myself, is there such a leak that costs so much? Now if I wanted to find this how would I do it myself? Any help would greatly be appreciated as to I am retired and on a very fixed income.
October 10, 2008.

Cycle key on off on off on read codes in the odometer area
P#### let me know what you have
check gas cap if loose or if she got gas with the engine running may cause check engine light to come on

need manual CHECK IT @

Oct 14, 2008.