All film-forming clear finishes I know about fail due to UV from the sun. Problem is that they peel, requiring a lot of work to prepare the surface to re-coat. How about 100% tung oil, thinned with mineral spirits? It won't form a film, but will make the wood look beautiful. And you just re-coat with more of the same when it begins to fade. It's what they used on the teak decks of submarines in WWII, and they saw some harsh conditions. It won't be your low-cost option though.
“We should be careful to get out of an experience only the wisdom that is in it and stop there lest we be like the cat that sits down on a hot stove lid. She will never sit down on a hot stove lid again and that is well but also she will never sit down on a cold one anymore.” - Mark Twain