You do not need a guide. Your deer tag will run you around $300.00 not $200.00. There is no law being discussed that I know of to require a guide in the future. Even if it was proposed I doubt it would pass. Eastern Montana is the best place to hunt mule deer. The down side is that it's nearly all private, but through what is called the Block Management Program, you can gain access to more land than you can hunt in a season. If you want to know more about Montana's Block Management Program follow this link.
I have to agree though, that the best way to start out is either with a guide or a local willing to take you out. Feel free to ask any more questions if you'd like. I'll do what I can to help answer them.