budget system for f150

Where do you plan to purchase all of this from?  I found the amp for 500.00 on sounddomain.  At 500 its hardly budget.  If you want a cheaper amp recommendations I think they could be found for you, for example two of these saves you 250 over the Hifonics and provides the same power:  https://www.cardomain.com/item/JBLP1802

I would skip the second set of coaxials and get a cheap sub, it will round out your system much better.  In fact I would not buy coaxials at all, I would get components.  However if coaxials are all you can afford now then get them, and move them to the rear when you can afford a set of components upfront.  Give us prices so we can gauge what you are getting for your money.

For example, a cheap sub and amp: https://www.cardomain.com/item/BLAPCA10COMBO 100 for both.

Just a cheap subwoofer, use the the 4channel or the JBL to power one of these and you'll be rocking the cab of your truck: https://www.cardomain.com/item/BAZRSW1024DVC   https://www.cardomain.com/item/MTXT8104A    https://www.cardomain.com/item/MTXT8124A  dont recall if that truck has the bench seat in the rear, if it does you should be able to make one of those fit.  NO! you do not need two subwoofers.

If budget is in mind, then keep the coax speakers but buy the ones to properly fit, in this case a 5x7" for the front and rear, not a 5.25". DKE168 for the current model. Th ebetter option is to keep the stock speakers in the rear and upgrade those later. Instead, use the $ from the rear speakers and throw it towards 6.5" components for the front. They will fit, a mounting adaptor must be made. Model # DSE216 to keep it MB Quart. This is probably the way that I would go myself. I would rather buy something once and keep it rather that buy it to change it out later on.