I came up with a pretty cheap but really good setup that has worked for about, a week solid. First get a ramp or a hill (Hard Part). Next take a short haired hallway rug, go to the local thrift shop, i got it for like 5$. and then a orange snow bank fence.
 http://www.homedepot.com/p/HDX-4-ft-x-100-ft-Orange-Barrier-Fence-998044/100384030#.UVjkdRyIM3k you don't need it to be extremely long. Put the rug down, then the fence on top. Screw or staple it down. If the rug is short enough, then you should get pretty good speed going down. Much faster than a full sheet of turf, and somewhat cheaper.