Percentage Formula - customer field

Percentage Formula - customer field

Hi I am trying to create a customer formula field.

We want to input a sales price of £500.

If the Lead Type is 'Self Gen' we want the formula field to work out 60% of £500 i.e. £300.

If the Lead Type is any other type of lead we want the formula field to work out 40% of £500 i.e. £200.

Please can you tell me the formula I need to achieve this, thanks, Jamie