It's not an uncommon fault on cars that sit about a lot.... Which if its a 10YO car with only 20000 miles on it it has sat arond a lot, and I'd guess not in a nice warm garage.
Anyway a new front brake caliper for a corsa is about £50, you also need a new set of pads and then it's most likely at least an hr labour charge from a garage , which can range anything from £50/hr to £100/hr..... So get a quote.
If it is the ABS , which is another possibility... it could be the sensor, they are about £12 each, and they are easy to change, but can be a fiddle to unbolt if the area is dirty/rusty,... The sensors are plastic, but they are bolted through a metal hole and they are not greased from the factory. ... but if its that, then the ABS warning light should also be on.
The ABS sensor ring could also be the problem .... Early ABS rings are just open to the elements, cos its cheap to build. they look like a cog with a million teeth, these can get corrosion build up which the sensor then reads wrong.... It can be as easy as a wire brush job to clean it up.... but if its gone to far you need a new one ... they are about £8.
Assuming its any or even all of the above ,for any home machanic its a couple of hours to sort and cost less that £100 for everything... In a garage you are paying for a shop to be open and someone wages... So if you aint confident or don't have £500 woth of tools and a garage to work in, then its shop prices.
I wouldn't go to sell it with a dodgy ABS, cos if you trade it in the garage will assume the worst option to repair, and knock a £1000 off easy... And selling it privatly to an individual, with an undeclared known fault is a legal nightmare.
Depending on the problem, its quite likely if one side is now 'faulty' the other side will be very soon ..... might be worth asking to have both sides looked at while its in the garage ..... So all in both sides and VAT ..... I'd say under £500 should sort it.
