It depends on the store that you buy it from. On Amazon.com, BeWild GLOW IN THE DARK Spray Paint is $7.99. Sp@z Stix "Solid White" Glow Backer Spray Paint (3.5oz) is $5.49 on amainhobbies.com and ClearNeon Spray Paint is $19.95 on raveready.com.
Historically, glow-in-the-dark paints were made with radioactive elements which actually posed some health risks. Chemiluminescence and photoluminescence are behind the majority of glow in the dark products.
In recent news, one group in the Netherlands is coming up with innovative ways of making the roads safer. Design firm Studio Roosegaarde and Heijmans Infrastructure have teamed up to introduce ideas for a so-called "Smart Highway," incorporating ideas such as color-changing road paint, glow-in-the-dark lane markers and interactive street lights.