CouponPress does the job on a budget, does take a bit of fiddling to get it how you will want it and you may want to strip away some of the code.
Depends if you want something automated as I find couponpress doesn't work well with icodes when automating, but maybe thats just me.
I have a custom vc site that I can sell you the code, but you would be looking at low x,xxx. See the site in my signature to see how it looks/works. The code would give you everything to automate it, create custom merchant descriptions etc, newsletter signups and more.
By couponpress is a fraction of the cost and if using for a small niche code site then will be a much cheaper option.