I have tried jiggling the steering wheel, turning the steering wheel forcefully each side, overriding the transmission to change the gears, spraying WD 40 into the cylinder, and lightly tapping the cylinder with a hammer. Anything else I can do, or does the dealer have to fix it? And if so, how much will that cost me?

What year?

I had an Avalon ignition cylinder replaced. It was very expensive. I took it to a local dealer (we don't have a Toyota dealer in town), and he replaced it, but to get it to work, he had to tow it to the Toyota dealer in a nearby town who fiddled to make it work. It cost me around $600.

Check for a faulty automatic transmission gear position switch. See if this link offers any help, even though it's written regarding Hondas the concept should be applicable:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-3.html#post258005

I would also test all under dash and under hood fuses with a test light or multimeter, if the key is stuck.

It's a 1995 Toyota Avalon if that helps. WHOA, $600??

It's a 1995 Toyota Avalon if that helps. WHOA, $600????

That quote may have had other work done and probably included towing and/or new keys.
The O.E. part price is around $100.00 and should take about an hour or so to replace. Slightly more if the lock cylinder needs coded.
Note: if equipped with Remote Keyless Entry/Theft Deterent, the replacement keys are very expensive: about $200.00+ each, plus programming.