cost research 

hardware

only some computers have a good enough spec for game design as others will crash the cost for one of the good ones range from around £800 plus.peripherals is things that you can plug into a computer like a mouse or a keyboard you don't really need a expensive keyboard or mouse as they are not as important as the computer but you may need things to record sound like a microphone for the sound on your game. dev kits are needed to allow creation of a game mainly for the platforms like consoles such as Xbox and play station.

software

the software is important for game design there are many different ones the main ones are udk unity game maker and Maya. game maker is for 2D  games but there is costs for different versions

 and unity is the main one used for mobile phones apps and tablets.

 the udk engine and game maker are free but im not sure about the others. 

PUBLISHING

you can publish many different ways for different platforms the problem is the cost of the publishing
for you to pulish a game you need =either a dev kit for xbox or psn or team but to publish a game it can cost a good couple of hundred pound maybe up to a thousand.