I want to open a Roth IRA with Vanguard, but the minimum is three thousand, which I don't currently have. If I were to open an IRA with Sharebuilder (or some other institution with lower minimums) would I later be able to transfer it to Vanguard without paying fees for cashing it out?
Yes. It is very easy to do a direct custodian-to-custodian IRA transfer.