What is the cheapest & best RC-toy for parts ??
-Has a simple circuit like just forward and backward options.
-No streering needed.

Additional bonus features:
-Interference protection.
-Good Hz frequenzy.

Good and solid basic frame RC-circuit for experiments

 

Really depends on what type of experiments you plan to do. You can get very basic RC's under $20, but they are typically run by a single circuit board that has everything on it, making it less useful for some experiments. An entry lever "Hobby Grade" RC is maybe going to run you close to $150, but has separate components that will allow you to swap out different components as needed. I do a lot of my electronics projects on RC cars and planes, and I would get bored pretty fast with a cheesy $20 RC special. What kind of budget are you looking at?

I'd look on craigslist for a used hobby grade RC if your budget is really tight. "Traxxas" vehicles are great for experimenting, super durable, and almost all local hobby shops stock parts for them.

For new, this is not a bad deal: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXAAMW**&P=ML . And there is a $15 0ff code on the main page for ordered over $125, so it would only be $115 plus shipping.