Barb, I used a 1 amp panel as detailed at my site
http://my.tbaytel.net/guskers/

Check the section on the solar panel.  The 1 amp panel I've installed (in
conjunction with a charge controller) would run around $150 US.  It keeps
both batteries topped while the van is sitting (not a daily driver).  While
camping, I haven't had a problem with 5 days of lights, stereo, etc off the
aux which is just another standard lead acid battery.

I did add a 12Volt flourescent fixture which is much more efficient than
the stock lights.

Don't bother with much smaller panels...my experience with several is that
they are useless for automotive use.  My goal here was primarily not to
worry about external charging during idle time/winter storage, although the
panel certainly helps while campling.  With your Optima, I suspect this
setup would be fine.