Pienza or Montepulciano would both make terrific bases, but Pienza might be slightly more central for you since it is closer to Montalcino.

I've seen good reviews of this apartment in San Quirico:
http://www.intuscany.net/apartments/...o_costanti.htm

It rents by the week, but if it's still available, they might settle for four nights.

For places in Pienza:
http://www.portalepienza.it/

I've stayed in the Il Giardino's smallest apartment and paid 45€ per night in Sept.2008. While I wouldn't want to stay in this particular apartment again (lack of comfortable seating and bedroom up stairs), I would stay in one of their other apartments.
http://www.ilgiardinosegretopienza.it/

Another good website for lodging in the area is Crete di Siena.
http://www.cretedisiena.com/english/

For Montepulciano:
http://www.prolocomontepulciano.it/index.uk.php

Thanks to everyone we have secured lodging in Montalcino with a kitchenette and a terrace. We are super excited. And now we will have to include some time in San Quirico!

I really love how all you Tuscany-experienced travel rallied around for rtbotts in her dilemma. And rtbotts - looking forward to your report back, so we can all cheer your successful outcome! Enjoy every minute (and every glass!)

So glad you have your lodging settled, rtbotts. Through your post, I have been able to get some great suggestions for our upcoming trip. Thanks to everyone who contributed.

I promise to share a report on what is looking like it will be an amazing trip!

What is the name of the place you booked in Montalcino?

Residenza Palazzo Saloni

Thank you for helping us find it.