It depends how involved you want to get. Absolute minimum would be a printer, a computer/pad to design the stickers, sticker paper, and scissors to cut out the stickers.

If you want the stickers to look good outside for more than a few days, you should laminate the stickers (add a clear protective layer). This can be done by hand or with a machine.

If you don’t want to deal with making the stickers, there are (in the US) a lot of online companies that you can send your design to, and they will print the stickers and mail them back to you. Price will be determined by size, kind (regular, vinyl, color, etc), and how many you order - the more you order, the less each sticker costs.

Search for “custom stickers” to get started.