Replacing the rubber and gaiter usually required dismantling the suspension components to some degree. That can take time and be much of the labour quote.
From what you say, I don't think your indicator bulbs are at fault. it sounds like your rear light lenses might have faded. That happens sometimes with age and the indicator/brake lights then appear too white. They must be the correct colour to pass the test. There is a liquid on the market that you paint on the inside of the lens to return the colour. Failing that, you may need to replace the lenses. They are about a tenner from scrapyard (depending on the car). Maybe your quote includes sorting the lenses out.
Be careful swapping the tyre with the spare. If you put the worn tyre in the boot as the new spare then you can get a ticket for having a defective tyre which is 3 points plus fine. You would have to leave it out of the car - but then you are up the creek if you have a puncture!
Other than that, the labour and cost don't seem too bad for what you say. It does depend on what exactly they are going to do - and don't forget the Vicious Added Tax is on top!