Just got a 95 f150 300 inline. It's got this spot on the fender. What are my options? Should I fix it? What's it gonna cost?

 

Rust is car cancer. If you don't fix it, it will and get much worse. As far as cost, take it to a body shop and get a quote.

 

You have some catching up to do before you're on my level.

I did order a set of patch panels for my rear fenders. If you, or a friend, is able to weld and you don't mind doing some cutting/fitting/painting, it's not that expensive to fix. Here's the link to the set I bought Ford F150 F250 Pickup Bronco Truck Bedside Panel Pair | eBay

Alternatively, if you're really cheap, and willing to put slightly more work in, you can cut your own patch out of a piece of scrap sheet metal (Did this for my tailgate, huge pain for shaped areas)

The body shop would be the easiest/quickest fix, but it's your choice. Good Luck!