Since cashflow is an issue, here's my advice:

* Get the rewards from someone else. *

There's no need for you to pay for these perks. Find partners in complimentary fields, and approach them with the offer that you will connect them with your buyers list (a very valuable thing) in exchange for their rewards.

When it comes to Cost of Customer Acquisition, this could be an incredibly smart thing to do from the reward provider's viewpoint. They get access to proven buyers in the related field for whatever their rewards cost...and they can figure out how to make money and Lifetime Customer Value from that pretty quickly (some from your list are going to buy from them...CCA = $X rewards...LTV = $Y bought... LTV - CCA = margin per customer.)

"It's not magic, it's math!"