I don't know how long they have been available, but anyone noticed that Raspberrypi.com do cheap antennas?: Mnfr product code SC0480 .
It is intended for the Pi Compute Module 4 according to the datasheet, but that's no reason not to use it for other purposes.
The antenna is approx 108 mm long. The supplied cable has about 180 mm of coax between the end connectors.
The cable has a U.FL connector at one end. Annoyingly, the other connection on the cable/antenna is reverse-polarity SMA (i.e., RP-SMA) and not normal SMA (it's because these are low-cost consumer antennas, so RP-SMA will prevent users from attaching higher-gain antennas to the connector. Still, it's a bit weird because I thought most Compute Module use-cases would be industrial/enterprise, not consumer-oriented).
Still, not bad for the low price if you need a WiFi and/or BLE antenna.
