Hello there,
Sounds like you might be new to online advertising?
I'd love to work through it with you and teach as much as I can while trying to grow your biz.
First things, when you say "pay per sale campaign" there's a few options:
You can pay per lead, per sale (commission or affiliate) or a success fee.
In general, if you're paying an adwords agency or freelancer it's a straight $% on top of your ad spend. Typically around 10-20% of total ad spend. Thus if you are aiming to spend $1,000 per month on AdWords, add 100-200 for fees.
Couple questions for you, do you have a website? A sales funnel? What kind of products are you selling and in what niches?
If we can sort out some of that I can tell you more honestly if I can help or not, but need more info!