marbles

I was thinking about getting my kids a marble building set/marble run  for Christmas.  I want the kind that are basically blocks with a hole or groove for the marbles to go through. I want them to be able to build it lots of different ways, so they can get creative.  Does anyone use this as a handicraft?  My kids love building with legos, knex, etc. So, I think this would be a hit.     Anything I should look for when purchasing?  The creative type sets are pretty expensive!  Of course, the ones that are pre-built are cheap!  But, I don’t want those!  Any ideas where to get one cheaper? 

Thanks!

Jennifer