Wow that is just crazy! As a former disgruntled employee of Best Buy, I say STAY AWAY!
While I am a fan of good ole' hardwire Ethernet any day over wifi, and agree with the guy to mention it, here's the reason he did. $$$$. Best Buy's business model is all about the upselling of additional services. When reeling potential customers in, my dipstick of a manager told me to give the cost of all of the additional BS services as a three year plan, if the customer balks, take it down to two years to make it look like you want to save the customer money. Sounds like they're doing something similar with you. Did you ask them what it would be for just coax, not Ethernet?
Last year at work we opened up three regional offices around the country, two utilized existing buildings, one was a brand new build and was slated to be larger than the other two and have multiple training rooms and conference rooms for employees and customers alike. I called the builders and got a few recommendations from them of companies they know of that deal with data and voice wiring in the area, and then got a few quotes. The outfit I decided on was not the lowest priced, but had awesome reviews. For 28 CAT6 lines, a patch panel in a wall mounted network rack, the mounting of three ceiling projectors with both HDMI and VGA cables fished through the walls, the total coast came to a few dollars under $4200 for all parts are labor and don't forget that was for a commercial building.
Here at our main facility in Upstate NY we have a local one man business that takes care of our Ethernet and phone wiring. He charges $35 for a site visit and $60/hour. All cabling and ends are included, things like amplifiers, wall plates and junctions boxes are not.
Things I would not allow Best Buy to touch: My house, my car, my computer, my garbage can, the weeds growing in my ditch.