How long is a piece of string?
To take your questions bit by bit.
I have a share in an aircraft that is single engined IFR capable - cost was £10K. I know of another for sale that is £12K. Both 1/5 shares. Running costs whether it's IFR capable or not are the same - the avionics don't contribute to the cost of fuel and servicing in the big scale of things (Except when they go wrong - but that's not often).
How many hours - how good a pilot are you? That you don't know yet because you don't have a PPL. I would suggest that you learn to walk before running. I've just done my 3rd IMC renewal with no problem, but probably 1/3 of my flying requires the use of IMC skills (as opposed to actual flying in IMC, though there's quite a bit of that too).
My suggestion would be get your PPL first and forget about IMC at the moment. Once you've got the first part sit down with someone who has an IMC and uses it (there are many who don't) and discuss with them what it needs, in relation to your (by then newly learned) skills.