What is the best way to adapt/convert my mono blocks & JJ243 preamp to Bluetooth so I can to listen music via my iPod/iphone?  I have seen items from $30 to $300.  
Thank you,
As you've discovered, there are scores of Bluetooth receivers available. Two that are well reviewed are the Auris at $119.
 and the audioengine B1 at $189. Either should work well and give you sound that's as good as possible with Bluetooth as the means of transmission. I don't have experience with either but a friend owns the Auris and is quite happy with it and I own an audioengine D1 DAC that works well in my shop system.

Very happy with BluDento.

Receives stream from Bluesound Node. uses BurrBrown dac, amp VTA70, elekit 8500 preamp, elac debut speakers. Overall this setup is more worthy than its current designation for the work out room :-)
I own the audioengine B1. Given a higher bitstream (at least 256 kbps), it sounds pretty good.