You will be really lucky, like lottery winner lucky to find an 8' bed F150 sitting on a dealers lot thats not an XL stripper contractor type.
I wouldn't go by whats sitting on the lots as a price comparison. JMO but it seems like most dealer are loading up the F150's as they're more popular and lead 1/2 ton sales. If you go to Fords build and price site, you'll find that you can get an F150 for way cheaper than an SD diesel.
If you build identical XLT trims then no way they're the same price. For one, the F150 is cheaper to start with and the diesel option is $9K or so. It's virtually impossible for them to be the same price if you compare equal trims levels.