Lp Electrical

Depends on the location but the testing will cost £150 upwards usually. consumer unit will cost £375 upwards normally. every property has different issues to overcome when doing these works.

Usually about £150 - £250 for the supply, just depends on the use of the shed, that determines the size of cable, and also where you are taking supply from, if the consumer unit backs onto an exterior wall that is a but easier than if its in the middle of the house.

It depends on what you consider acceptable yourself. the model is irrelevant as you can / could purchase that model unpopulated and build it to suit your needs,

any consumer unit that is not metal will attract c3 observation codes to do with fire resistance. new 18th edition consumer units will be metal therefore contains any potential fire better. new consumer units supplied since yours were installed but prior to the metal requirement would have had complete rcd protection.

when inspecting and testing a property according to napit observations guidance you would give a c2 - urgent attention required - to circuits which are not rcd protected, under the heading i would suggest ' where cables are embedded in walls less than 50mm ' basically every circuit in your home will be embedded in a wall less than 2 inches. so therefore all circuit require rcd protection.

there are other observations such as probably at the time your board was installed they came with knock outs to allow cables into the top or bottom. this is not allowed anymore, you cannot push a 1mm2 wire into any part of the consumer unit.

these are just a couple of examples, in the case of these examples,
if you can retro fit an rcd in to cover your original circuits, and rectify the holes in the consumer unit then it is possible to bring it up to code, some sparks wont do that, and that is up to them. some will try to rectify. another reason that the old circuits were not put on an rcd is because whom ever was installing it was worried that putting the old circuits on a more sensitive device like an rcd would cause nuisance tripping as existing faults would show, where they do not on an rcd.
there are a lot of possibilities.
i cannot see you consumer unit, but it may have so many observations, and no capacity for the rcd upgrade and therefore it may be just as easy to install a new consumer unit.
the reason you are getting conflicting information is because different sparks will have different comfort levels with what they feel happy to sign off an declare safe. before doing anything get the old circuits tested.