Oh who said STi?
No doubt the garage have said that the running costs are around the same as your clio (if they did they would be lying!) as you will need to take into consideration a few factors before even attempting to buy an Import STi.
First of all, the car only runs on SUL (super unleaded fuel) and octane booster is advisable (approx 3 quid a bottle per 50ltrs of fuel).
Servicing is a bit of a culture shock from a clio, its every 6 months or 7.5k (which ever first but still 6 month even if you only do 3k per year).
A Major service can set you back around 500 quid, most are around 300 and the cheap intermediates will cost you around 90-100 quid. Expect to spend a lot on your car, modifications and imports dont really match as there have been a few cases of melted pistons etc as the fuel gets leaned out too much so an uprated ecu is advisable even on exhaust modifications (like a decat, and ecus can cost around 700-1200 quid).
Brakes are a weak point, the 4 pot calipers on there aint too bad (assuming that its a relativly new STi) so there are a few options open to you.
I would personally look at spending 8k per year (age dependant) on insurance, fuel, parts, servicing and general maintenance. (yes it does acutally cost this much!)
My final word is do not skimp on parts, get the best available to you (tyres etc) otherwise you will end up with big bills......