To make Flash games, you need Flash. It does cost money. If you, or a sibling, is in school, you can get a discounted price on it. Just look for academic pricing. Just be prepared to spend around $200 for the student version, or about $900 for the professional version. One more thing, don't attempt to get the newest version illegally, you'll undoubtedly end up in trouble.
Any student is eligible for the academic pricing. Just search 'academic software' on Google. Academic superstore is one of the bigger sites you can get the discounts at.
Flash is from Shockwave Flash (.swf), the original company who made flash (now it is Adobe) Flash makers are available through mostly the internet and some office stores. Also, there's a flash maker called LiveSwif, however, It doesnt support ActionScript and is allaround terrible.