Why can't I find a reasonably priced Rear Drivers Side Door Lock Actuator for a 1997 Toyota Camry?

Lol because your definition of "reasonable" isn't what they cost.

You can't find one for the price you want because you aren't in charge of choosing how much to charge. Some bigwig is.

If they have all the supply then they can charge whatever you want. If you need the Part bad enough you'll have to give in and just pay it.

Supply and Demand. They have the supply you have the demand.

They also don't go out very often. So anybody would be reluctant to make/sell them as there won't be much of a demand.

It's kind of like why I can't find a Reasonably Priced Ferrari.

So you have to either do without, or buck up and pay the unreasonable price because you have no choice.

Call your local Toyato dealer. He can fix you up.

have you tried looking for it at your local junkyard? maybe even ebay . ..