Hello CRB, Welcome to the Forum. If you are intending using the machine for monocouches only and you are set up in a gang of 3 or more lads the G4 is a nice simple machine to use and by far the most popular plastering machine in the world. Consider the machine is also a big bit of kit and so vans and storage must be considered. A site where you dont have to take it home everyday is ideal.
You will need a generator most probably to run the machine as it is powered by 3 phase.
A Brand new G4X smart all set up complete with everything you need inc 25 mts hose will cost shy of £6.5k plus vat. That is including training. A Generator is likely to cost about 2.5k plus vat.
If you are in a gang of less than 3 regular men and would like to introduce machine plastering to other applications then a PFT Ritmo is worth considering. They are single phase and much smaller than the larger 3 phase machines which means you will be able to carry the machine from job to job on your own. By having the smaller machine you will be more likely to choose to use it more frequently on you different jobs without having to consider power issues and logistics The ritmo may perform slightly slower than its 3 phase collegue but in a smaller gang you do not need to put on as many mts so it makes no difference there, however if your gang did grow it would still mix and put it on the wall 3 times faster than any plasterer and labourer could ever do but saying that why would you pay a spread and a labourer wages if you could just get someone to spray and someone to fill the machine at a cheaper rate.
Ritmos start at around £5,750 for all the kit plus vat
The more bags you intend using per week should help you choose the right machine.