How much to charge for designing a collection of leather bag

Please help!!
I need to know how much to charge for designing a collection of leather bags for mass production

Well the answer is, ‘how long is a piece of string?’

How big will the collection be?
Do you think the designs will be simple or complex - will they take you a long time or not?
Dos the client expect designs only or specs?
Does the client expect a lot of research - eg. do you have to find materials, for instance.
Does the client want you to follow it up - i.e. will reworks and admin be included in your quote?
What is your experience? A rookie usually charges quite a bit less than someone with a track record.

The collection will be about 6 paces: of briefcases and attaché cases.
The level of complexity is of 50%, some will be traditional some modern, and the preliminary design should be submitted by mid January.
They expect designs only
The research will not be significant
There is an expectation of follow up, probably one time adjustment
Good experience, 3 years in house for a prestigious British company.

Isn’t the design considered a form of intellectual property that is of some value? The company is going to profit from your work for many years to come.
I assumed the reason some companies pay royalties was because they prefer to pay royalties, instead of high up front fees.
Simple hourly rate dos not seem to take into account the log term benefits of the work.
I know some people do not consider design an intellectual property, you could consider it an industrial design right instead.

Royalities is a really dodgy area to go into unless you trust the client 100%. A current client of mine is good to me and always pays me on time but I was witness to him comissioning another designer on royalties only then not paying him a penny even though the product sold. As the designer lives abroad, he’s not likely to see the shoes concerned in retail stores. They told him they didn’t sell anything!
How do you know they will be telling the truth when they tell you how many pieces they have sold? Perhaps if you go down this route you need to put something in the contract requesting the paperwork from sales?

Most clients expect the intellectual property to be theirs once you’ve done the work and been paid for it. Many will stipulate that you put this in the contract.

I’m not sure how much to ask for a project like this, perhaps a recruitment consultancy could give you an idea? They can be quite helpful as they usually know the going rate.

I’ve friend who designed on a freelance basis for lots of prestigious designer labels, Mulberry, Armani, lots more, she charged $400 a day as a freelance, but I think you might consider charging more than this.