soon to be married

hey,

i stay at Los angeles CA and i have my tourist visa here, i am still legally here and i'm engaged to be married, now my fiance was born in the US and she is a US citizen, now i dont really know how to start with the imigration stuff i dont want to be here ilegally and i want to feel the forms and send them before my i-94 expires, i want to be in the process time before it expires.
I tried to look trough your database of the FAQ's but couldnt really find something actually got lost, if anybody could direct me to the right place i will appreciate it.
I looking for info about the exect forms to fill out, the amount it gona cost me to the whole thing, the time it gona take for geting the working visa first then the green card and so on...and if i have to do stuff that i still dont know, need all of that info and help from you guys.

another thing is do u think we can do it by ourselfs or do we need to hire a lawyer?

help will be highly appreciated.
Thanks.