Adding a line, swapping phones, swapping numbers...! Keeping unlimited!

I would like to grab a little advice if possible. Currently my plan has 2 smartphones grandfathered in with unlimited data. Neither phone has 4G LTE capabilities. Our neighborhood just received 4G and we're eager to get the service not only for our phones but for our internet too. (Our cable service is $50 per month for a 5MB download plan and 512KB upload) Here's our plan to make this happen.

Phone 1: Droid 2 Global (Upgrade available)
- Upgrade phone to Samsung Galaxy S3 with 2GB data cap
Phone 2: Droid 2 Global (Upgrade available)
- Buy a cheap 4G LTE phone off ebay and swap the D2G for this new phone
Phone 3: NA (New line)
- Start a new line with a purchase of a Samsung Galaxy S3 with 2GB data cap

So we'll walk in to Verizon and make the above changes. We'll then also swap the phone numbers with phone 3 to phone 2. This should make both of our regular lines 2GB data plans with the cheap 4G LTE line having unlimited for our internet on a line that will never actually receive calls. Our Verizon plan should go up by about $35 after adding our 12% employee discount. The 4G at my place gets about 10MB up and down. (Confirmed on a friends Galaxy S3) I confirmed this should work over chat with Verizon reps but we all know how reliable that is sometimes...

The real question is what cheap 4G LTE phone should I buy? Any 4G LTE phone that allows me to install Foxfi or another tethering app would work perfect. As long as it can take advantage of the speeds the tower offers. Verizons cheapest 4G LTE phone on their site is the "Pantech Marauder". Looks like it's $50 to $100 on ebay. Would this phone work? Is there an older phone that would work as well? Thanks for the help and let me know what you think.

It's this or we have to buy 2 Galaxy S3's off ebay for about $450 each... Which is actually tempting as well. After 12 months of paying $35 per month, the two ideas are equal in cost. Except we would actually keep our grandfathered plans and wouldn't have contracts. After 18 months, we would be in the same situation now but instead we would have S3's instead of D2G. The savings from using Verizon internet would completely cover the cost of the phones. This of course assumes Verizon doesn't kick us off unlimited data by then.


EDIT: After all that, I decided I wanted to buy them retail. We managed to snag a blue and white 16GB on ebay for $430 each. One is new the other is basically new.