Here is an inexpensive and sturdy kayak trailer. Start with a 5x8 utility trailer. We were lucky to find one without a floor for $329.99 at Northern Tool. The price reflected a discontinued model. Look around in your area. You'll need the 5 foot width if you want to transport four mirage kayaks! Bolt two carpeted 2x4s on frame cross members with (4) 5/16" bolts. The carpeted up-rights are also 2x4s and are 36"high.
Put a 2x4 brace between the up-rights for support from the wind. 
By adjusting straps, you can transport from one to four mirage kayaks very securely. We have two OB's and two Rev's. We positioned the Rev's on the inside for better turning radius. Don't think it is necessary and if you do have a problem, an extension for your hitch is an easy fix.
After purchasing the material to convert our utility trailer into a kayak trailer our total investment was under $400.00!