If caught in a thunderstorm outdoors, get into a hard-topped vehicle or building; avoid ridges, lone trees, water surfaces, and metal objects

No monetary cost. The downside is that your trip gets interrupted for at least half an hour. The real challenge is actually turning back when the thunder is still far away.

There is no safe place outdoors within the range of a thunderstorm. It is only considered safe 30 minutes after the last clap of thunder has passed. The National Weather Service in the United States states: you must run into a sturdy building or a hard-top vehicle. Tents provide no protection against lightning, and open-sided picnic shelters are also unsafe. Cave entrances and small rock protrusions are also dangerous, as electric arcs can jump across gaps. Hiding under a tree is the second leading cause of lightning-related injuries and deaths. If you hear thunder, you are likely already within the lightning range: "When thunder roars, go indoors."

美国国家气象局. 户外雷电安全：「There is no safe place outside when thunderstorms are in the area」「Avoid open fields, the top of a hill or a ridge top. Stay away from tall, isolated trees or other tall objects」「Stay away from water, wet items, such as ropes, and metal objects, such as fences and poles」；实在走不了时「If you are in a group, spread out to avoid the current traveling between group members」；恢复活动「Wait 30 minutes until after the last rumble of thunder」；「Remember, a tent offers NO protection from lighting」「Do NOT seek shelter under the beach picnic shelters」「Cave entrances are dangerous during thunderstorms. Small overhangs can allow arcs to cross the gap」. https://www.weather.gov/safety/lightning-outdoors；美国国家气象局. 雷电安全：「If you hear thunder, you are likely within striking distance of the storm」「When Thunder Roars, Go Indoors」. https://www.weather.gov/safety/lightning-safety；美国国家气象局. 雷电误区：「Run to a substantial building or hard topped vehicle」「Being underneath a tree is the second leading cause of lightning casualties」. https://www.weather.gov/safety/lightning-myths

Tents, gazebos, trees, and rock protrusions do not count as shelter. Hard-top vehicles do count. Convertibles and motorcycles do not, which is a conclusion the author drew from the condition of being "hard-top." Start retreating as soon as you hear thunder; do not wait for the rain to start falling.