I am guessing $200ish for a reese style hitch on the Jeep (you might get lucky and find a used one)
Northern tool has a cool "fold up" trailer for $289 that is 4' x 8' but you will note the overall length is 134" [11'2"] so with your kayak, the front could stick all the way out the tongue when you secure it!!
They will give you the needed paperwork to get a tag for it and I think you have to buy tires (which they have too, prob another $100 or less)
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_465468_465468
So for the same $500 you would have something you could do a heck of a lot more with!!
One final note...I didn't look to see what you have...but if a Wrangler..be careful. Short wheelbase is not the best for towing...but the trailer weighs under 300lbs so it should be good! (With a light weight load/kayak...you may actual have issues with trailer "bouncing around" since very little weight on it?)