Normally they will give some discount codes in support site, but it is a low discount code.
If you want to have more high discount codes, you can visit review sites or affiliates site.
For example, you can find one discount code here: mobileleak.com
(Please remember to scroll down the page and you will see the checkout links with 35% discount).
Updated on Dec 2018: please try to use this code for discount
Discount 30% for new customers.
Available from 1st Dec 2018 to 1st Dec 2019.
Apply for Paypal method only.
How to apply the code: https://www.mobilespyfaq.com/hc/en-us/articles/360014960794-3-How-to-apply-a-discount-code-coupon-