From where?
ARIN? Well they do not exactly sell IPs in the first place. They allocate IPs based on your needs. Also, to get something like 2000 IPs from ARIN you need to be directly getting your bandwidth from a tier-1 network (have your own connections and fiber running to your routers, network)... no colo or middle men
If you are getting your 2000 IP blocks from a large network provider (SWIPing, sub allocation, etc).. I'm surprised they are giving out such huge blocks. I'd imagine they'd give out IPs in /24 blocks.. If you are buying 2000 IPs from them at regular intervals.. I'm surprised you are not dealing with ARIN directly.
Also.. no network provider is going to give you 2000 random IP addresses. They always address in blocks.. and I am imaging you are talking about a /21 block which has 2046 usable IPs.. So there is no such thing as a 2000 IP block..
Sorry, if you claim certain things you may want to back them up. We use around 5000 ip addresses and we've never aquired IP addresses in 2000 ip blocks.. So I just find that a bit hard to believe