I just bought Gyeon Wetcoat (500ml) for a little under 20$, it's a spray sealant. You can find similar sealants from Sonax, CarPro, etc.
Washed the car, light polish with a DA polisher, wet the car again, spray a panel with Gyeon Wetcoat, blast it with a pressure washer. I used it on my wheels as well, beads pretty nicely. You have to apply it on a wet surface and you can't let it dry out. You can probably find application guides on youtube.
From the various reviews, should last a few weeks to maybe a few months. Not bad for the ease of application and low cost. The 500ml bottle should last me over a year if I apply every 2-3 months.
If you want something more durable, there's always ceramic coating. But prep is harder and quite tedious. I leave stuff like those to professionals