New Math, it's what my business partner did.
Cost to purchase 6s 128 GB using the Best Buy Method
$424.00 (includes tax)
BB site also says $35.00 Verizon upgrade fee if true that would be $460.00
Activate new iPhone 6S and wait for it to show up on the My Verizon portal - wait about an hour, and don't use it - make sure your contract is extended and UL data remains. Then power it down, remove the SIM and put the SIM back in your trusty iPhone 5. Flip your iPhone 6 for roughly $700-ish dollars. Keep your UL data at the current price for 2 more years, with about 8-10 months of data paid for by your iPhone 6 sale price difference.
Two happy campers. You with the phone you like and the plan you like, and the person rocking your now-former iPhone 6. One grumpy camper - Fran Shammo, VZW CFO (that's Customer F***er Overer).
To the Best Buy Method n00bs - do read the slickdeals first post. I'm not going to regurgitate any of it. I've done it 3 times, and I'll be using my last and 4th upgrade shortly. There's one step to take upon arrival of the iPhone - take the iPhone 6S out of the box, remove the SIM card and cut it up then throw it in the trash. If anyone activates that SIM, your UL data will likely go the way of the Dodo Bird.
One add. There's a Car Toys near where I live. One of the reps told me that they'll sell you an iPhone 6S and use an upgrade, then let you walk out the door with it - still wrapped and unactivated. YMMV.