Keep putting money into my 1999 Four Runner?

Hello!
So happy to have found this forum.
My Four Runner has 148 K miles.
The engine light has been on, and off, for years.
Each time I've had it looked at, the check-engine light would come back on after a few days.
I was told that it's probably a loose seal at the gas cap.
Moving forward.. I just left my car off to have a new timing belt put in, and a new water-pump, since they will be in there.
Additionally, they're replacing the valve gaskets/seals because Its been dripping a little oil.
That brought my repairs to around $2K.
I'm having my electric antenna repaired, as it was broken off a few months ago, and the rear key hole was pushed through, so that needs to be repaired, as well.
It is 20 years old.
So at that point, my total estimate was at around $2,400.
As I was getting ready to leave, the gentleman suggested I have my engine diagnosed, because the engine light is on. Another $145.00.
I'm trying to decide when enough is enough.
I'd like to hear from some other Four Runner folks re: this issue.
Also, I'm wondering if anyone else has replaced their own electric antenna, or rear door key hole, maybe with the assistance of YouTube.
Tx much.

 

Fake news Toyota's never break. Lol. What are the codes from the CEL?

 

The antenna mast is the easiest too fix. Just pull the old one out and it retracts the new one when you turn your radio off. Make sure they do the grommets when they change the valve cover gaskets. They come in the kit usually. Let them do timing belt and water pump. Drop a new front and rear O2 sensor in and rock it another hundred thousand miles!!!

 

I’m goin in for my last emissions test in August