If you are looking for a price to sell second hand, then as an idea my brother just bought a SLG10 with 48cu tank, proto tank protector and a Viewloader Revolution Eye Force for £150.
The marker was listed as £110 on it's own. Here is the thread if you want to check it.
I bought a proto on/off for £15 and a PMR spares kit for £25 with solenoid on here too.