Well done for finding a reasonably local Sierra
I think the price you paid is about par for the course.
Even my local breaker will pay £200-£250 for a dead large saloon car, I guess this is part of the reason as to why donor cars are selling for decent money.
I remember the last Sierra I stripped.
Had a word with the breaker & explained why I would be bringing it in with no vehicle ID.
He said he would be able to take it in as general scrap, asked him about all of the interior & plastics, he said bung it all in together.
Cut the shell up, loaded the whole lot into my truck, took it to the breakers & got paid just over £100 ( Not bad for a rusty load of old crap )
That was a few years back, scrap prices have probably gone up since then.
If you have the means to get the remains of the donor to the scrapyard, there is a fair chance that you'll get a nice chunk of your money back.
That said, if the body shell is in good condition it may be worth good money for someone looking to re-shell a project car. ( Would imagine that early models are quite scarce )
Enjoy the test driving of your new donor.