If you have a limit of $90 to start a business (I would totally recommend you invest that money if that's all you have, hypothetically), and you can't exceed this amount, you would write it as the following:
Let's say "b" represents Business
You may write this 3 different ways.
b=$90
b<$90 (meaning b is less than $90, this is my least favorite way, as it doesn't quite capture what this question requires)
b is less than or equal to $90. This site, unfortunately, does not allow one to use the sign that represents "less than or equal to", but I'll give you a picture of what it looks like:
The sign that means "less than or equal to" is the MOST accurate way to show that the money you have for your business must be LESS than, or EQUAL to the said amount, which is $90.