@antiflag ... congrats bro ... for being a satisfied mini user 
for oil change i go to total cng engine oil ( 4 litre ) 20-50 .. blue color dnt remmeber the price .. they also have oil filter .. cost around 200 - 300rs ...
why changing steering oil ? auto gear oil ? u having any problem with them ?
if not then just keep them on level that it .. no need to change it just add if it's less then required ....
do check brake oil too
i dnt have air filter in my mini so i dnt know the price of it ... i have installed air intake ....
u also changing spark plugs ? i have seen split fire plugs they person was asking 1800rs ( 4 plugs ) for it ... at fair sale auto .. plaza .. saddar ...
for air filter n stuffs u can go to allianz auto located at plaza saddar ... opposite to hasmi auto .. across the road on main road ....
do post pics of ur ride : )
waiting for them ...
regards