Can I expense the purchase of a video drone for marketing purposes for my Schedule C business? If so, what category?

The purchase of a drone for your business would be entered as an Asset to be depreciated and not simply expensed in a particular category.

When it is entered as an asset, you will be given the option to expense it as a Section 179 deduction, but it needs to be reported on your return through this method. 

Even if the acquisition cost is $900? Or could it be deducted as an expense?

Yes - If the drone costs less than $2,500 you can take it as an expense using the de minimis safe harbor election, instead of depreciating it over several years.

Please see this TurboTax Help article for taking the de minimus election:  What can I expense or depreciate with the business safe ...