There's a bunch of reasons why you might want an audio variometer. These are amazingly useful little pieces of technology if you don't plan on doing 'sled-rides' for the rest of your life...
Here's some currently available audio-only varios, listed below. There's not a huge amount of variation in the prices. As usual, don't hold me to these prices since they are only a guide, which will soon be out of date.
Get a second or third-hand audio variometer if you can, this is one piece of paragliding gear that your life doesn't depend on!
And of course anything electronic tends to get cheaper as time goes by.
As is my habit on this site, I've organized the info to make it as easy as possible to compare.
Vario Model: Mini Vario
Weight: ??? developed 1991, but probably still pretty light
Dimensions: ??? but is meant to be mounted 'in your helmet' :-)
Power Source: 200 flight hours on the battery, what's the bet it's the same Lithium as all the others...
Vario Model: Sonic
Weight: 46 g (1.7 oz)
Dimensions: 89 x 35 x 18 mm (3.5 x 1.4 x 0.7 inches)
Power Source: Lithium CR2450, 3V/500mAh, good for around 200 flight hours
Vario Model: IQ Sonic
Weight: 40 g (1.5 oz)
Dimensions: 89 x 37 x 19 mm (3.5 x 1.5 x 0.7 inches)
Power Source: Lithium, probably 3V/500mAh like the Flytech, good for over 200 flight hours
Vario Model: Solario Mini Vario
Weight: 36 g (1.3 oz)
Dimensions: 54 x 36 x 21 mm (2.1 x 1.4 x 0.8 inches)
Attachment: ??? probably Velcro
Power Source: The massive spheroid thermo-nuclear device around which our planet orbits