I would like to know how much it will cost to install electricity to my wooden garden shed, which is about 30ft from my house. Also, what I will need to purchase.

Hire an electrician... if you have to ask these basic questions, then you really don't know the answers to the far more important ones you never thought to ask.

Call a couple of electricians and get prices. You should not have to get or do anything beyond signing a check.

Lots of vague questions. Cost depends on how much power needed, conduit? Direct bury? How far from breaker box to shed? As noted, get 3 estimates and go from there.

Do you have an idea what you want to have at the shed? A light and a couple of outlets won't be a big deal, since you can run a single circuit with a small direct bury wire. But if you intend to run multiple outlets or other loads requiring more than one circuit you will need a sub-panel. I suspect you just want some convenience outlet(s) there and a few lights so it's not a big project. But until you are more specific with your needs it's vitrually impossible to tell you what to buy. But the other posts just may be the best advice, hire someone with the qualifications to take care of this. If you are willing to do some of the back-breaking work, such as digging the trench, perhaps ​you can save a few bucks.