Sounds dodgy. That's why myself with the help of a consulting alarm engineer are increasingly doing project work to help clients act on FRAs and drawing up a spec and getting quotes and going though them with a fine tooth comb- we've saved client's tens of thousands of pounds.
Get another quote - I rarely go off one alone and don't use the big players who are often (not always) the ones with the massive quotes (& closed systems so you are then stuck with them for the next 10-15 years)
I don't agree with the whole "being stuck with them for the next 10 - 15 years" thing - once your out of your first year there's absolutely nothing to stop you going to a
competant fire alarm company (not a PAT testing outfit) and getting them to do it on a "test and report" basis,with fault finding knowledge - yes,if you need to change the config you may have to get them back but that's a "changing the configuration" issue and there should be some control over who can do this (this is changing more and more with the software being made available through on way or another).
Usually when the bigger companies are the larger quote it's because it's a project not within their normal or targetted customer base and where a "fire alarm out of the box" from Welsh Wales will do the job to meet the required specification but in this case there shouldn't be much difference if you use
good equipment.
The whole protocol debate is pushed by the companies who either make panels or make heads but not both.That doesn't mean that they make bad detectors or panels (in fact,I'd stand over Apollo products over any of the third party stuff) but they may not be able to offer as practical solution for a particular project as a company where everyhthing is "in-house",it's all specific for that system and the R & D invested reflects this.