Currently, if you have an unrooted Droid Ultra, Maxx, Mini, X running Kit Kat, FoxFI only works with USB or bluetooth tethering (i.e. cannot set up a hotspot). If you root, there are options.
However, to root the Ultra/Maxx/Mini/X you need to still be on Jelly Bean (4.2.2) and run some exploits first. With the X, there is an exploit to get back to 4.2.2 so you can root and the upgrade. With the Ultra/Maxx/Mini, once you update to Kit Kat, you can't go back. So if you want root, make sure you read up on XDA before you accept the update. This may not be an option for long as they're probably start (if they haven't already) shipping them with Kit Kat already installed.
Of course, you could get a Developer Edition (i know the Maxx has one, not sure about the Ultra and Mini) which would allow you to unlock the bootloader and get root.
Verizon offers a Max plan (not to be confused with the Maxx phone) for folks still on unlimited data. There is a 8 Gb with tethering plan for $50. If that compares favorably to your current rate, that may be a good option as you can skip all the tinkering around above. You can also purchase your phone on the Edge program to spread out payments and get earlier upgrades.