I'm looking into buying a dedicated server and running a couple of servers from it and I was wondering how much data an LFS server uses. Most have a limit of 1500GB per month and I'm pretty sure that would be way more than needed but I thought I'd check here.

Depends on
1. How many players you want on it in total
2. What Packet Per Sec you set it to run on
3. How full you expect it to be on average

Oops, knew I'd forgotten something.

Going on patch W here:

Players: 23
PPS: 4
Should be empty most of the time but what about full 24/7?

189.8KB/sec

Which equates to:
(189.8*60*60*24*30)/1024/1024 = 469.171143GB upload

Pop on a tad more for leeway and you should be ok.

Just remember if your hoster doesn't provide bandwidth monitoring, you'll have to do it yourself.