Putting in a receptacle is a pretty simple job, and can easily be DIY for probably under $150, but research proper methods and do the job right. First thing to do is get a permit from your city building dept. This will ensure the project is inspected, legal and done correctly. Your friend cannot hire out to do the job unless he is a licensed electrician, but he can still help you, the homeowner do it. The trench will need to be minimum 18" deep if using conduit which I highly recommend. You can instead choose to use a UF type direct burial cable if you dig the trench deeper but conduit is inexpensive and worthy of the extra cost.
Three quarter or even one inch PVC conduit is very economical, easy to work with and large enough to easily pull in the wires plus give lots of room for expansion if ever needed. Install sweeping 90 degree bends at each end of the conduit to feed into and out of the trench and attach the conduit to a weather proof box using a threaded fitting. At the pool end I like to set a post to mount the weatherproof receptacle box if there is not a structure such as a deck or shed already there to fasten to.
Wire size and type is very important. You will need THWN wire, one strand in black for hot, one strand in white for neutral and one strand in green for ground. Wire size will be determined by the distance. For a short run of up to 40' from the panel 12 gauge wire will be plenty for 20 amps. For a longer run of say 40-80' up-size to 10 gauge wire for the same 20 amps to prevent excessive voltage drop. You cannot pull any type of jacketed "romex" NM cable into conduit, you must use wet rated cable and THWN inside conduit is the right choice. You can feed power to the new receptacle directly from a spare breaker in the service panel or from another receptacle or circuit, provided adding an additional receptacle will not overload the circuit. Also note every outdoor receptacle is required to be GFCI protected.
Some codes are pretty universal but you will want to check with the inspector for proper trench depth or other particular requirements for your area.