Gary,
I know what it's like to live on a FIXED income, and I also know the value of a dollar. I have been using synthetics for the past 20 years, Mobile 1 at first then switched to Amsoil. Mobile 1 use to be a very good quality motor oil till they passed the OIL FRAUD ACT, and allowed the oil manufacturers to claim 100% synthetic oil when it really is a 80% mix. Mobile 1 diluted their oils to save money, or I should say to make more money, and allowed the quality of their product to be compromised. I have been with Amsoil for the last 8 years and have not had one reason to complain. Amsoil has some very nice products, and I use a good deal of them. For the diesel, I use the Series 2000 0-30 weight. For the cars (and some are turbocharged) I use the Series 3000. For the running gear it the premium gear oil, ATF, and synthetic grease. I really like the synthetic grease, it protects better and last longer then conventional grease. I use it on all cars and trucks, as well as the ATVs , Trailers and tractors. Speaking of ATVs, we have three (Rap tor,Blaster,and Lakota) and I use nothing but Amsoil products on them. For the 4-stroke's I use the Amsoil 4-stroke motorcycle oil. And in the 2-stroke it's the 2-cycle racing oil, this stuff is great. It makes less smoke, doesn't foul the plugs and makes considerable more power. We also use the Amsoil Gas octane booster in them, and Series 3000 oil in the gearbox. The Amsoil grease really protects the A-arms bushings, I run in the creeks and sand, and it's very hard on these areas. For the rest of the Air-Cooled engines, like the lawn mower, 3-generators and Gas-welders, I use the Amsoil 3000 motor oil and have no problems. I also use the Amsoil products in our Air-Compressors and Hydraulic equipment.
When using Synthetics, the most important thing to remember is to allow plenty of time for the break-in process to accrue before you switch to synthetic engine oil. I generally like to allow 4-5,000 miles for a gas engine, and 7-8,000 mile for a diesel. Smaller engines don't need near that much time, for mowers, generators, and compressors 3-4 hours is fine for break-in. ATVs and Motorcycles need about 5-6 tanks of gas for break-in.
Synthetic oil has a much higher initial cost then conventional oils, but the added protection, increased fuel economy, and better performance far off-set the additional cost. Generally I have gained 1-2 additional miles per gallon by switching to synthetic oil's, my best gain on a gasoline engine was 4 MPG, and it was on a Mazda rotary engine. For me, the drain interval that works best is I change the oil twice a year, spring and fall. And I change oil filters every 2000 miles, and then just top off.