heres some random ones.
http://FantasticContraption.com/?designId=1930116
http://FantasticContraption.com/?designId=1897912
http://FantasticContraption.com/?designId=1931071
The steel ones really aren't necessary to beat this game. I didn't use a single one XD
And yea, try making the money limit just a teeny bit lower. I beat level 8 with more than $4000 to spare.
I'm sorry, but this game is way to easy. I tried a Guru song the first time ever playing, and I cleared it with a 71 max combo. Since this is for fingers, and the player's reflexes are faster, I would say it has to be much much harder.
 "Fantastic Contraption")
 "Death Dice Overdose")
 "Super Crazy Guitar Maniac Deluxe 3")
 "Sonny")
 "Amorphous+")
 "Tangerine Panic!"){kind=icon}
 "Feel the Beat (F2Jam)")
 "FWG Bridge 2")
 "Flash Flash Revolution - Kongregate Application")
 "Kongai")