Currently you can stream Doctor Strange through Disney+, which can cost as little as $5.99. There are loads of great Marvel movies like Doctor Strange available to stream through Disney+ so check it out.
Currently you can rent or buy Doctor Strange through Amazon Prime Video, or you can rent or buy the movie through iTunes or Google Play. You can also rent or buy the movie through YouTube.
If you're streaming the movie through Disney+ you'll have to pay the monthly cost of Disney+, which is $7 per month. If you want to buy or rent the movie, you can rent it for as little as $2.99 or buy it for as little as $13.99 from Google Play, iTunes or Amazon Prime Video.