Obviously, you have to work out the taxes for where you live. My sales tax rate is 6% and I get charged that on the subsidized price of the phone and on the upgrade fee.
Right now a subsidized iPhone 5s 16GB is on sale at Best Buy for $150 and if you signed up for the BB reserve gift card, you can get it for $100 + tax. So for me, it would cost $140 after taxes and the upgrade fee. Since the Verizon iPhone 5s is GSM SIM unlocked, you should be able to sell one of those mint/new on swappa for a minimum $550. To be safe, let's say you sell it for $525. After swappa fee, paypal fees and shipping insured/signature required you can net $475. So after you subtract the $140 you paid for the iPhone, your profit is $335.
If you live in California you get taxed on the full retail value of the phone when you use an upgrade so it may or may not be worth it in California; you would have to do the math.
iPhone 5s at Best Buy using reserve gift card, factoring in upgrade fee, current sale price and 6% sales tax = $140
Moto X Dev Ed including 6% sales tax at current sale price = $403
Net from Sale of iPhone 5s assuming sale price of $525 after you pay swappa fee/paypal fees/shipping = $475
$475 - $140 - $403 = -$68.
So you would end up with a Moto X Dev Ed for $68. However, if you score yourself a Motorola Admiral off of ebay for about $25 and do the tradeup program for the $100 gift card you net $75 on that.
Remember the Motorola TradeUp program requires that the Motorola Admiral have a clean ESN, work and not have a cracked screen. There are lots of bad ESN and cracked screen cell phones on ebay so read the listing when you purchase.
Then $75 - $68 = $7 so if you are willing to do the TradeUp program, too, you end up getting a free Verizon Moto X Dev Ed and a profit of $7!
Caveat - if you use the Motorola Tradeup program you have to select Moto X all other carriers, not Moto X verizon if you want a $100 VISA prepaid card. I did this with a Verizon Dev Ed purchased from Motorola directly and got the confirmation that I am getting the $100 VISA prepaid card.
If you didn't sign up for the BB reserve gc, the Moto X Dev Ed would end up costing you $43, which isn't bad at all. In fact, the current price for a 32GB Moto Maker Moto X using your upgrade is $50 + $30 upgrade fee = $80 + 6% sales tax = $85. So even if you didn't sign up for the Best Buy reserve gift card, if you are willing to sell an iPhone 5s on swappa and get a Motorola Admiral off ebay for $25, you not only save $42 over getting a 32GB Moto Maker Moto X, you get yourself a Dev Ed with an unlockable bootloader (which you can't get using an upgrade anyhow).