Book time is probably an hour a side. That's got to be a minimum of £120 a side plus VAT
There's no way this side of the moon that that job is being done correctly.
I’m using a main Vauxhall dealer who knows my car, and I know their management team. Therefore. I know I have redress if they get things wrong, and anyway on a car that is 23 years old and hardly does 3,000 miles in a year, I just want what is easy to do; that is a professionally outfit doing the work whilst I keep in the warm and dry that now I must do for age and health reasons 
Nobody is saying paying somebody to do the work is a bad idea. None of us are getting any younger, and I'm still sporting an injury from changing a wheel last year

But there is an old adage, if something is too good to be true, it probably is. The price sounds massively low *IF* yours still has self levelling.
Hence, I urge you to just check (nothing strenuous, just getting down on hands and knees to check (or photo, if unsure) the base of the shock). It's possible in a former life, its have the SL removed, in which case that price doesn't sound low at all.
Given that I believe SL springs coupled with a non SL shock will dramatically impact handling in an unpredictable way, I really do urge you to do this simple check, and if you have got SL shocks, contact your dealer and check they know this.
Obviously, your car, your choice, so I will say no more on the matter. But I think we'd all be sorry to hear you'd reversed it into a hedge, or worse, because somebody who doesn't know Omegas put the wrong combination of parts on.