I don't know what you mean by "A Bell helmet would cost me at least $700 for a full face one." It took me 10 seconds on Google to find a Bell Hornet M2005 for $130. But I admit, I've never heard of a Hornet before. I think Bell Sport and M4 are the most popular.
I personally have an open face Bell MAG5 Pro SA2005. Every club I know allows 2005 helmets until 2016. I believe they all allow M2005 as well as SA2005. But there are some clubs that don't allow open face, so you have to make sure.
This place has discounted SA2005 Bell helmets:
http://www.thebellstore.com/Auto/auto.html
This place has the 2010s.
http://www.helmetcity.com/page/HC/CTGY/bell