Looking for finish line help

I've had numerous people ask me about building them a track and as much as I'd like to sometimes time is an issue but just as much an issue is figuring out what to do for a finish line. I'm considering building some small foldable tracks in the 8 ft range to fit a table top.  I've got the starting gates down, just need finish lines. 

Have any of you guys built or experimented with a paddle/flag type finish, similar to the HW one from years ago?  I'm trying to keep my costs down to sell it cheap so anything electrical is out. Not to mention I don't have the patience or knowledge to mess with it. If 3D was still making his I'd go that way because it's worth it and parents wouldn't hesitate to pay a little more for a quality finish line. 

Any suggestions would be appreciated.