I used 2x8's for the ski guides, screwed 1x2's on both sides to guide the skis, and used a 1 7/8 x12 LVL for the track ramp. Screwed 1x2's across the LVL to match the track spacing for traction. Bought extruded aluminum ramp supports at Sears.
Total cost about $100, about an hour and a half work to assemble. Have been using them for 9 years now, a few times a year, still in brand new condition
One tip, use a ratchet tie to hold the center ramp to the trailer hitch, otherwise your track will spin it out from under you and you will be left with the skis on the tailgate and the back end of the sled on the ground
Never had a single problem them (other that dealer giving me a hard time when taking in for maintenance, because he wanted to sell me a trailer)
I don't use the ramps when unloading, just pull the sled back and drop into the snow