This seems to me to be a job that does not require a specialist (I would certainly use a roofing professional for actual roof construction issues) - I could do that sort of work as DIY, so it means any good odd-job man (or woman) should be able to do it. But your issue is finding a good odd-jobber! You will need to watch him/her to check (1) The gutter is placed the correct way up (seems like a joke - but is not) (2) The gutter inclines slightly down towards the drain pipe (I am just guessing that this makes sense) (3) Correct caulk (sealant) type is used - otherwise you might later find the job was done with an indoor sealant. I reported recently here about a relative having two workmen fitting an automatic washing machine and leaving the transit bolts in (which I pointed out to them before they finally placed it) - later found they also cross threaded the water connection (it is plastic to metal so is easy to do if you are stupid and do not tighten by hand initially). If you use an odd-jobber then be extremely careful in this country and if you use an 'expert' then be extremely careful in this country!
AGN Jamesvan, Banilad Hwy. 09154201724 Probably not the cheapest, but well organised and professional.