What's the most cost effective or cheapest way for high availabity on Oracle Standard Edition One?
With dbvisit you can maintain a standby database, in a very similar way as Data Guard does in the Enterprise Edition. You might want to check this out. The setup is very easy, support is good and the pricing is very reasonable, if not, cheap.
I blogged about it a few times, 

see how to configure dbvisit to manage existing standby database running SE 

and Cost reduction using Oracle SE and dbvisit standby 

I hope this helps,
Ronald.