1999 Camry charcoal canister and control valve

I have the same 1999 camry. Here’s a recent history (engine light comes on):
1/24/2007 Goodyear Auto–replaced Evaporator canister and control valve $549.19
7/12/2007 Goodyear Auto–replaced Purge Solenoid valve $134.24

11/8/2008 Toyota Dealership–Replaced Charcoal canister and Purge Valve (Toyota says they still have to charge this) $656.75
2/9/09 Toyota Dealership–Estimate today for Replacing Vacuum control valve–for $135.00
I have not authorized the work yet.

I know people are rolling their eyes at the work I had done to this car. I asked friends (who do their own auto work) and I try to educate myself. I really don’t know what to do. The Camry has 89k miles; I still love the car. But the cost of repairs is starting exceed what I think the car is worth. Any ideas? Advice? Suggestions? Thank you, everybody.