accord 2000 code P1457

I am new to news group, so if this topic was discussed before, please just
let me know how to search for it.

Anyway, this is my problem:
few month ago, "check engine light" came on. Honda dealer diagnosed and
checked the car and did not find anything wrong (2x), just reset the light
and replaced the gas cap.
On my third visit, tech pulled evap leak code P1457. (Wander why I had to go
there 3x to find it).
They found: sticking vent shut valve and canister, and gave me price $375 to
fix it.
I do some work on my car. I think I food the valve under the car, just in
front of the gas tank, next to the fuel pump.
It does not look like a big job to change it. Anybody did this before and
how much are the parts (vacuum canister solenoid valve and the canister, if
it should be changed too?