If frugal is the key point here, then I'd skip the DSP-5 switch and get a single tune
Maybe just a tow tune if the truck does work. And make sure the tuner knows you're deleting the DPF.
That'll save ya a couple hundred right off the bat, the tow tune would probably net the best economy but economy and mods don't "always" go hand in hand.
Get the cheapest exhaust you can that deletes the DPF, that's why I mentioned diamond eye, as last time I checked their prices were the cheapest and all the exhaust is doing is moving gases, it doesn't have to be expensive. Between the PPE intake mod and the DPF delete and 4" exhaust that will probably be where you'll gain economy.
I mentioned the minor fuel supply mods cuz you're going to be demanding more fuel with the new tuning and the stock filter doesn't filter down to a small enough micron level.
With the added power comes added trans stress, and the Allison is finicky, and can't take much more in stock trim than 60whp before you can cause issues. At 90+ WHP things can get dicey and it's kinda luck of the draw and how you drive, so I'd highly reccommend the shift kit, for even tow tunes can reach 90whp over stock power. The Allison is a great trans but it does have limits and one of them is it's a learning trans, so it stores shift values then predicts needed values for the next shift. This is great except when you want to change power levels on the fly, which is one benifit to just getting a single tune.
So, $1300 to spend-
PPE intake mod- free
Tune- 250
TransGo- 100
Fuel filter and filter kit- 65
Exhaust- 300-400
Ported rail and hi flow CP3 kit- 100
You're at
$815-915 give or take and various shipping charges probably will add up to $1000!
That mod list falls into your spending amount.
You could afford the DSP-5 tune and switch, but that will give you enough power to damage the trans if you're not careful, but it is fun to have the power! Just remember he trans learns and you don't want to switch to the race tune at a light and mash the to pedal
