That said, there are a lot of resources out there now (convertible note generators, "standardized" series AA paperwork, etc.) that can lower this cost substantially if you try. Wilson Sonsini has a note term sheet generator [1], and there are probably others.
Also, keep in mind that many reputable, startup-savvy lawyers will work on a deferred fee for this kind of thing. You can also negotiate prices for simple contract reviews.
[1] http://www.wsgr.com/WSGR/Display.aspx?SectionName=practice/t...