Why does nobody talk about how a $12 timing light saved me $900

I hit 300,000 miles on my 2003 Tacoma last month and finally put a timing light on it for the first time. My idle had been rough for about a year and I was ready to drop $900 at a shop in Fresno for new injectors and a tune up. Instead I borrowed an old Craftsman light from my neighbor, found the timing was off by 4 degrees, and it took me 15 minutes with a distributor wrench to fix. The truck idles smooth now and I feel like a total idiot for not checking it sooner. I get that modern cars don't have distributors, but anyone running an older motor should own one of these. What else am I sleeping on that's under $20 and can save me a shop trip?