you will only remove the first ip, if it's not directly send via server.
so if you use smtp, the header will contain the ip of your personal internet-connection, each hop will add another ip to the header.
it's not a problem to remove your own ip, since the first hop then will then be the mail-server
it's the same as if you would use a webinterface directly on the server to write your mails.
it's not that of a big deal to remove this line - just some regex in the postfix settings.
though i don't know any provider who does this.
what about buying a small vps and implement it yourself?
this will probalby be only a bit more expensive than $2, but using some lowend-system you should be able to do this within 5-7 $ per Month (perhaps even a bit cheeper, if it's not "offshore")
