You should be testing at least one new product every day with a minimum of $5 per day for 3 days, so over the course of 10 days you will have tested 7 products for 3 days each totaling $105.
Some of the ads you may kill after 1 or 2 days (not 3), if there are no conversions or add to carts, so the spend maybe less. You have to be looking for and adding products to test every single day.
On the basis above your $700 will last you around 45 - 55 days and you will test roughly 45 - 55 products. Bear in mind these are guesstimates and far from the exact numbers.
The key point is having a strategy to test every day. Start with the first Facebook strategy
which explained in the atricle. Take your time and get at least 5 products researched before you start testing. Then continue to keep adding to them until you find a winner. You need to be consistent and stick with it.