i am not 100% sure but i dont think BMW sold E30's with a M technic kit on them. if it was put on, it was aftermarket.
if you do indeed need a new steering rack, my last E30's was replaced prior to my owning it. the previous owners always went to the BMW dealer for service. they replaced it with a refurbished rack for almost $1000, keep in mind tho, this is the bimmer dealer parts and installed, if you take it to someone else it will be cheaper, and if you do it yourself its all parts like dudesky said.
in respects to buying an E30, they are awesome bimmers. you just have to be careful because there are plenty of abused ones out there. and versus a newer honda civic, you will definatly pay less to maintain the civic than the aging E30, but you get what you pay for. with the E30, you get an awesome drive, a strong engine, powerful brakes, solid suspension, and a classic Bimmer