Once you see street painting as entertainment, it then makes sense to treat the chalk artists just like you would a band. Some events want a lot of featured artists, and others only want 2 or 3. It can work either way, just make sure that the artists you bring in are really good at chalk art, and will be good ambassadors of the art form and actually "entertain" while they are on site chalking. They should provide photos to be used for advertising the upcoming event, and be available for interviews with local press. They can also be brought in a day or two early to lead a street painting workshop for local artists.
Artists need to eat, too.
There are a couple of ways you can compensate chalk artists. One is to approach the artists, explain what you want and request a quote for their services. The quote should include travel costs, food and art materials. You also need to remember to include any street cleaning, barricades, security, tents, and other items in your costs when figuring out the total costs. Some events will arrange for lodging, since they get special discounts or donated rooms from local hotels in exchange for sponsorship acknowledgment.
Offer a Stipend.
Another option is to offer a stipend. A set amount would be given to every artist that is invited, and they can use the money for their travel, lodging, materials, food and whatever else is not covered by the event. This seems like the most "fair" way to do it, but it makes it harder to attract artists from father away, since their travel costs might be too high.
The event should include a light breakfast, coffee and juices, cold water, lunches and snacks each day. Most featured artists will bring their own supplies and chalk.
It's also nice when the event has a party or get together on the evening before the event for the artists and sponsors to get together and mingle. When the artists are working during the day, it is tough to have time to talk to everyone, and a pre-party is a great way for everyone to talk in a more relaxed atmosphere.
The event should either arrange the artist's flights or travel and pay for it, or advance money to the artist ahead (half up front is normal), so the artist can purchase their flights. The rest of the amount due should be paid at the end of the event directly to the artist.
What not to do?
Don't charge the artists fees to participate or for anything (t-shirts, programs, etc.). Street painting is a physically demanding art form, and the artists take it very seriously. Many started by donating many weekends to the art form. Asking them to "chip in" is like asking a volunteer at an event to pay for parking and a ticket to the event.
The important thing to remember is to treat your artists well if you want to grow your event into a premier art happening. An event that respects and treats the artists as special and talented guests will become known as a special event, and you will have your pick of great artists.