It's not so much that the job is too small, but that it's hard to predict how long it'll take... and also that the customer often underestimates the work involved.
Are there cutouts in the existing worktop?
Is the sink undermounted or overmounted?
Is the wall behind the existing worktop tiled?
Is the existing worktop the same thickness as the new worktop? (40mm usually)?
Are there many joins in the worktop?
Is the existing worktop solid wood?
Solid wood worktops are installed differently to chipboard Formica type. An expansion gap should be left behind the worktop, of about 6mm to 10mm. This gap would then be covered by an 'upstand' (like a skirting board). The upstand should be made from the same timber as the worktop, although these can't be bought.. they must be made from rough planks (from Morgans Timber etc).
So there's the cost of the worktops, the cost of the upstands (timber and processing into finished pieces), and then the cost of calling out to measure up, time spent travelling to get worktops and upstands... then there's the whole process of changing over the worktops, and without seeing the current setup this is hard to predict. If the tiles were done after the worktop then these may cause problems. Someone has to oil both sides of the new worktop four to six times with oil... this will tke several days as it must dry between coats (Noyeks may have pre-oiled worktops).
Undoing the plumbing may be tricky (this is necessary to change over the sink and taps)... if the existing plumbing is dodgy then it could be very difficult. In other words, there's a chance that existing bad work must be put right before the new worktop can go in.. this is hard to predict in advance.
If the sink is undermounted then the cutout must be done with a router, .. I don't know of any other technique or tool that will produce an acceptable cut.
The worktop should be fixed at the front edge, and only fixed at the back in a way that allows for movement. (This can depend on the exact layout of the worktop)
So the job isn't as easy as it sounds.. .I'd advise that you find out exactly how the workers intend to install the new worktop before picking the cheapest.
You could advertise the job on TenderMe for free... you might get some responses.
Woodworkers are good for prices but I can't see them installing the worktop. There will be no comeback if you use a recommended fitter who messes it up (or at least I don't think there is)
Cheers so