Orange County is out of my service area, an Oakland REALTOR should really address your question. I'm sure one will come along soon... For now, please re-post and indicate particulars about the lot: what are the dimensions? Is it in a platted subdivision? if yes, what type of amenities does the subdivision offer? Or is it a lot in an established neighborhood? Is it near a lake/park/school, etc.? Is it a corner lot? larger than the rest in the neighborhood? Does it have a view? Is there anything negative about it--like: it's next to the retention pond? It"s smaller than most others in the neighborhood? will it have to be cleared? Leveled? Oh, lots of stuff like this... What ever information you can think of--the more specifics, the better! Best of luck and happy hunting!
P.S.-A paid appraisal is probably your best bet--especially since you're buying from friends.