The costs of hiring an electrician can vary a lot depending on where you live, your house structure, etc. As a rule of thumb, it should take them around 3-4 hours to perform the whole installation of a transfer switch and cost up to $500.
It's not uncommon though for homeowners to pay as little as $200 for the whole set up. That's why it's a wise idea to go with a recognized brand such as Reliance Control since most electricians know these switches extremely well and can install them quickly, saving you money on their labor costs.