Yup if you want to wire yourself there's better prices out there. I don't think you need to be an electrician but the time I get everything and wire it's worth the $90. 14 gauge cord for 1800 watts with two receptacles.
ETC Supply I've come go know will do specific wiring for the NEMA 1 plastic box as well - I had thought it was only with Nema 4x, so it's less if you don't care about the metal box. I believe the shrink wrap is really intended for the probe and the connection with the wire but doesn't hurt to do more. I have a heat gun so may just do that. But for $5 bucks mind as well have them lol.