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The replacement of a regular faucet is very easy. If you cannot get a grip on the pipe behind the faucet, you will need someone to stabilize this trom under the house. I Goggled outside frost free faucet and there were many returns. I believe that you can find the information that you need on one of these sites.
If you are at all handy with home repairs, I see no reason that you could not accomplish this task.
Is $250.00 the right price? It is for the plumber. Expect to pay around $20.00 for a new one. Even if this takes you five hours, you will be, in effect, making $46.00/hour.
May Saint Rooter bless your efforts. I wish you the best.
JayR