A flipper.Lots of questions to be answered.
Knowledge you posses?Metal working experience?Budget?
If you dont have sponsoring, and wanting to have a real flipper-like Chaos2,or M2 Im afraid this will be difficult on a limited budget and knowledge.And then Im not talking about the new generation of Launchers -with Gravity as example.

I did make several rams, and started with a 127mm bore 180mm stroke 10 bar version.
I garanty you that it aint cheaper than lurking around on Ebay,or trying your luck in the for sale tread on this forum.

In any case, if you need more specific knowledge,mail me.
Basic formula to build a robot
Time*money= Robot
The larger the amounts of time and money, the bigger the chance that the robot will do well-if the basic idea is good.