On a budget, Key West Day-Trip still earns its price.
Gas/tolls or tour ~$70+; do as overnight ideally
The drive itself is the attraction — the Seven Mile Bridge and turquoise straits are unforgettable, and Key West has Hemingway's house, Mallory Square sunsets, and Duval Street's party. The catch: it's ~3.5 hours each way, so a day-trip means most of your day in the car and only a few hours there — it really wants an overnight.