Replying to Speed In Backyard

So, I currently have a couple of rails in my yard, and really wanted to make a fairly good sized jump. I have the space, but I can't get the speed to hit a jump and even have some trouble on longer rails. So, what are some cost effective ways to get speed in the yard? I know about the bungee banshee, but I just don't have $150 to spare. Also, I would much rather not build a drop in. So, what are some ways to get speed in the yard, preferably using household materials? Thanks guys.