I've been using Estibot for a couple of years now (paid subscription) and I've never seen a discount coupon or promotion offered for the service. Even when I allowed my subscription to lapse I did not receive any type of "renew & save" marketing correspondence. In fact, when I went to renew my subscription I found that the plan I had been on was no longer available, and that the price for a comparative subscription had increased quite a bit (I now pay $99/month).
Are you primarily interested in Estibot's appraisal service or in its other research tools?
Cheers,
Entropy