The poles are ionic residential. 8ft and 18ft. List price £ 113.90. The pump looks like a shureflo £70. Large column filter with resin (refillable) £134. Maybe others have seen these components cheaper
If you get it for less than the cost of these parts you've done well.
Check that the tank is baffled. Very important. Stops water sloshing around. Also make sure you have transit size van as will need payload of at least 600kg's. Also, is the column filter suppied full? If not, it will cost you for resin.
I think that supplying all the parts is the easy bit. Fitting the tank securely and wiring up the electrics safely seems a bit more technical. Is he offering to do that as well? Or is he just selling the bits?