Delphi setup of 10-20 TIdhttp by anonymys proxy

We need to access internet anonymous with Indy's TIdhttp client by Proxy. VPN is not an option, it must be a traditional proxy. We need someone to find a good and cheap supplier to this service and set up the purchase for us. A rotating service where the outbound IP changes as often ass possible is preferred, perfect if it changes everytime the client logs in. Traffic will be (total for all 10-20 clients) +- 500 gb month. We have tried ourself to find a stable service with reasonable prices, but just got lost in the jungle that this is.