7 Month old bike needs £300 worth of parts and labour

I have a Ribble Sportive Racer purchased in July last year and done 6250kms. In recent months the bottom bracket has become rather crunchy. I looked at replacing it and am familiar with replacing Hollowtech BBs and have the tools, however this one is Pressfit. I neither have the tools or knowledge to replace it. I am rather disappointed with the quality of this design; though to be honest BB type was not an issue in my decision to buy. So I've taken it into a well know high street chain of bike shops for a service.

The service quote is £298.91 when the bike itself cost about £1100 just last summer. Apparently I need a new cassette (maybe fair, third chain) need a brake caliper (as the rear one is a little stiff from a muddy winter, I often put tape over the gaps as I've had issues like this before, but this happens every winter) need new headset bearings because there is about half a mm of play in the fork, apparently tightening this one up is not possible,) need new brake pads (though I have more at home and put new ones on a month ago,) need new bar tape (though I don't really give an eff about a few frayed tape ends) and need new cabling (though again the bike is only a few months old.)

I feel like they are taking me for a ride, they sent me a nebulus list of item codes which I had to look up on the website. I am sure the bike will be smashing if I pay for all this, but apart from the BB and cassette most of these things are just natural wear that will recur in a couple of months and would never cause an issue. The cabling is particularly egregious; it can't be stretched by now; it is like they can't index the gears incase they jab their little fingers. Just crimp it, the little bobbin they stick on the end will drop off after a week guaranteed.

I feel annoyed that I will have to stand there telling them why I think they are wrong or I don't need this or that, whilst they stand their sucking their teeth imply that if I don't get everything done that my bike will explode. I came in asking for a bottom bracket and service, just greasing and tightening and realigning a few things shouldn't require half a rebuild. If I have to pay this kind of money every six months I could just buy a mountain bike in Halfords and throw it away.

Thoughts gentlemen and dottigirls? Does this sound reasonable?