Replacement rear derailleur.

[wiggetty151]

I have the attached rear derailleur.

I would like a suitable replacement without breaking the bank.

I ride this bike to and from work which is about a 10km trip.

Im just after the cheapest, yet most reliable one available.

The chainset is 7 speed and the front 3 speed if that helps.

[Duck!]

Lucky for you there is no such thing as an expensive axle-mount (the type you have is axle-mount, as opposed to frame-mount, which bolts to a derailleur hanger extending below the dropout) rear derailleur. You should only be up for around $25; any Shimano 7- or 8-sp. derailleur will be fine, as long as you get the right mount type.