Attorney for a 1 off task to read over partnership paperwork

Can you guys please recommend how to find an attorney for a one off task? I'll be joining a startup as one of the founding members (CTO), but the other founders have already put in place a legal framework using a startup specialized law firm. I need the attorney to look over the ownership/share grant and the NDA documents to make sure I'm not being screwed over. This has unfortunately happened to me before. Also, how much should I look to spend in ballpark on something like this?