You want to run an app install campaign for one of your clients.

Bidding strategies help you control the overall spent with budget constraints.

There are basically two bidding options: Lowest Cost or Target Cost

1. Lowest Cost

The lowest cost bidding strategy tells Facebook to get the lowest possible cost per result, while also spending your entire budget. 

2. Target Cost

The target cost bidding strategy tells Facebook to get as close as possible to your cost target. This option is only available for app installs, conversions, and catalog sales marketing objectives.

In this case you need to have a "Lowest Cost" strategy as you want to achieve the following:

- Limit the app install at $9.00

- You know you can't afford a higher cost of $9.00 as it won't be profitable for your client

Keep in mind that lowest cost budget will achieve your costs results but might not get you results as you might be bidding lower than the auction requires for your ad to be competitive.

You should start with lowest costs and then could potentially move to target cost once you've achieved at least 50-75 app installs and you have a better understanding of real costs for your client. 

You should also move to target costs if you are not getting enough app install results with your first campaign.