Do you ever pay transaction fee to invest in a mutual fund?

I have my IRA account setup in Fidelity and I’m trying to invest a portion of my funds into a vanguard target retirement mutual fund. Fidelity checkout page shows a $75 transaction fee since I’m trying to invest in an outside fund. Is that like a one time fee to buy into the fund from that account or would I have to pay everytime I want to invest in the same fund? I would like to keep all my investment accounts in Fidelity but prefer vanguard fund for one of the accounts. Whats the best way to do this? Do you all stick to buying mutual funds of the same company where you’ve held accounts? #personalfinance #investments #401k