Sorry, I see you're looking for operating costs, so I'll do my best:
Insurance is now compulsory and is split into third-party liability and hull loss. Together you should be able to pay about £600 a year.
LAA membership will be compulsory and about £80 a year. LAA engineering fees about £120 plus annual inspection from a tame inspector ~£100.
Hangarage (it MUST be hangared!) would range from free barn in a local farmer's field to £3000+ at a popular airfield.
Airfield/flying club membership up to £500.
So you could be paying £400 a month before you have even flown an hour! By flying in a group you can reduce some of these fixed costs though.
Variable (hourly) costs would be a bit more friendly:
1800cc VW is well suited to the LA4A to give it a suitable climb performance, but it is a bit thirsty - I think 12 litres per hour, so £24 per hour AVGAS although you could probably get approval to use unleaded from a garage forecourt which is better for the VW, but more prone to vapour-lock.
Every 50 hours you'll need an oil change - say £20.
The engine should last 1-2 thousand hours, so factor that in to your costing, but you never know without hindsight which you have.
The more it flies, the lower the hourly cost, but be realistic - when you own the aircraft you can't turn-up and fly, there is always maintenance to be done and you should probably factor 2 hours on the ground for every hour flown, so if you have to work for a living you are unlikely to fly 100 hours a year.
Do not buy it if you can't afford to lo the price of the aircraft. It is also much easier to buy than sell aircraft like this. Even with insurance there is risk and there is no such thing as cheep flying, but if you do you will learn all sorts and have great life experiences!