Have you totted up the price of the parts an got quotes from a garage for the labour?
A pair of new upper arms is £170ish
sub frame £390ish but if you ring Rimmer brothers in Lincoln they may be able to do you a better price if it means keeping the car on the road.
Here is a link to a second hand one
https://www.ebay.co.uk/itm/333140896...EAAOSw67tiQbtE
The advisory about corrosion may not be the death nail for the items, they may be in good enough condition to save but the arms can go in between an advisory of one mot and the next mot.
how much is the labour?
It is not the hardest job to do the change the arms and sub frame.
I have changed the arms, springs, dampers and sub frame. Seized bolts are the danger.
pm mickyboy a trader here to see if he can do you a good sub frame.
macafee2