2000 Grand Cherokee Jeep Evap code

I have a 2000 Grand Cherokee Jeep 2WD.  I had my “check engine light” looked at by a car repair shop. They told me that I had an Evap code of P0043.  The mechanic said that the price would be around $300 to replace canisters, etc. Is this a good price? and what are the problems that this could cause with my car if it is not taken care of?