I’m totally disappointed in my ’97 Tacoma because in several parts of the frame I can push my finger into it. This is considered QUALITY construction? So now it’s a useless piece of @#$%^%^ unless welded.

Never drove it on the beach and it has 105,000 miles on it and runs good with little body rust. It’s rusted under the passengers door and from the spring hanger forward near the gas tank. I’ve been quoted $700 to $1000 for welding it up, depending if the tank needs to be dropped. Is it advisable to repair and if so how does one keep it from continuing to rust? The shop says it happens because road sand gets in the frame and holds the moisture so it rusts. TYIA

Get the welding done because you wont be able to sell it and it's worth too much to scrap it, then once you get it sorted get the chassis and inside of all panels sprayed with waxoyl.

Before waxoyling it, maybe an idea for you.
Get the underside sandblasted where there are any spots of rust on the chassis and when surface rust is gone, treat with rust inhibitor , and then waxoyl it.
If you waxoyl over surface rust, it may continue to rot from the inside out.