i have an e9. so, its very new and i've only clocked abt 1300km on it. monthly maintenance is stil minimal, infact, there is non except for fuel. the fuel consumption is quite high, i am currently running at approx. 6km/litre. The consumption also depends on how you drive the car. if you are constantly flooriing the thing, then it is pretty fuel consuming. jap cars are cheaper to maintain than a european cars. you have to follow the user manual on when to change you timing belt, oil changes adn etc. They have all been calculated and if you don't follow them, it will like cost you more in repairs.
there are endless aftermkt parts for the evos. mine is still standard except for the ice. however, the car will be going to the workshop today to get a turbotimer, BOV and some gauges installed. be warned that you WILL be tempted to modify the car as i believe that any evo driver will never stick to "standard".
good luck in your search. if you do decide on the evo, let me be the first to welcome you to the evo clan. otherwise, do visit us on and off. there are certainly many interesting stories and experiences to share, like the gathering coming up this weekend (i think i got the date right) in JB. although i am based overseas, i truly enjoy reading abt them and the pictures. (s9, if you are reading this, i am counting on you for the pics!!!)
if you need a car to get you by before you get your dream/the car you prefer, consider getting a fairly new second hand. with 9 months ownership, you will probably not lose much. make sure you don't end up with a lemon that you have to constantly fix or repair though. that would be a nightmare.