Do you have a factory roof rack on the explorer?
The standard starter kayak recommendation is the Perseption Sport Pescador 12 found at Academy Sports for the everyday price of $499.
However if you let us know what major city you are closest to we can point you to a kayak shop where you can test paddle various other boats.
Please keep in mind that you will need several accessories to be legal on the water. PDF (life jacket), safety whistle, visible white light if you kayak when a boat light is required, and a paddle.
Weight is more of an issue more so than length with an suv and kayak, as most* boats will fall with in reasonable weight ranges that are not too hard on the back and not breaking the load of a factory crossbar.
*Obviously there are exceptions which are rather heavy like the Hobie Pro Angler which is a $2,600 boat.
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Crappie Fishing NE Texas from the Camo Coosa since 06/2011