Ultra low power data collection - reading strain guage

I have a customer that needs to digitize the output of a strain gauge.  Their power source can vary from 1.6 to 3.6V and is capable of supplying no more than 200 uA.  Ideally, they want to use a differential input A/D and want a SPI output.  Sample rate is super low.  Maybe one sample per minute.  8 bit accuracy is acceptable.  The design is high volume 100-200K units and very cost sensitive  The Maxim MAX1391 is being considered.  As an alternative, I offered the AD7468 + AD8237.  I have a few questions:

• Do we have a differential input, low cost A/D that can operate at 1.6V?
• The 7468 datasheet recommend using the ADR318 as a reference/power supply for the ADR318 as a 1.8V reference.  This part is EOL.  I don't see another 1.8V reference to choose from.  Please offer suggestions of 1.6 or 1.8V references.  The customer does not want to use a higher voltage reference.
• I assume that if the reference can source enough current, there would be no problem powering the AD8237 with it either.  Do you agree?
• Can you propose any lower power or cheaper away to solve this problem?

Attached is my initial idea

A couple new thoughts.  Perhaps the AD8236 is a better fit for the Instrumentation amp.  It is much lower power.  Regarding the reference, I looked for something cheaper than the Maxim part and considered the following:

• TI REF3318 - $1.03 on Digi-key
• http://www.ti.com/lit/ds/symlink/ref3312.pdf

• Intersil ISL60002 - $1.12 on Digi-Key
• http://www.intersil.com/content/dam/Intersil/documents/isl6/isl60002.pdf

Both are very low power