You can bypass the “only Integers” constraint by adding a Float for the step option:
f.number_field :amount, step: 0.5
Update:
Actually you can use the value ‘any’ for the step, it will accept all floats and integers, and the step will be 1:
f.number_field :amount, step: :any
Update for prices:
You can use the rails’ helper number_to_currency to display a price inside a number_field:
f.number_field :amount, value: number_to_currency(f.object.amount.to_f, delimiter: '', unit: ''), step: :any