Is your key badly worn?Have you tried using a less worn key?

I have 3 keys and the valet key won't even work! My key that is not used as much as my wifes' key won't hardly work, so my wife just uses her key. She is afraid of being stranded. I did clean the cylinder with WD-40 and it did help. The dealer wants over $300
to service the unit plus parts. I am a mechanic, but I can't program the security system. WHAT DO U SUGGEST???

Sounds like the cylinder is binding up thats the one that need a toyota scan tool to program the key.Maybe you could swap out the cylinder in the toyota parking lot real quick and have them program it for you.Would be cheaper than them doing the whole job.