A reasonable quote will differ for almost any business, depending on what they stand to gain. Where a lot of agencies and/or freelancers are quoting monthly fees – I think it is better to look at the actual outcome and goals that you as a business owner is trying to achieve.
First of all – increasing visitors or traffic does not mean an increase in sales. So a better measuring point would be to increase conversion percentages per channel for example. So let’s say you’re getting 50 visitors per day or 1500 per month through organic traffic, and 2% of those turn (30) into enquires, of which 50 percent (15) converts over the phone – you are getting 15 new clients per month.
Consider the lifetime value (LTV) for those clients for your business, and see what an acceptable cost per acquisition (CPA) is. Doubling your visitors does not automatically mean doubling your sales. It depends on the quality of the traffic, which in turn is influenced by the traffic source and at what stage of the marketing funnel these new visitors are.
Are they just window shopping? Are they considering you VS a competitor? Are they returning to you after their research? The conversion rates of all three of these will be very different.
So to try and not go on too long – talk with the digital agency and/or freelancer to work in bringing more sales through the door by measuring conversion rates across the board. From the clickthrough rates on your ads, to the conversion rates of your landing page/ contact page – to even your phone calls.
All of these points can be worked on to increase the percentages, which in turn will bring you more sales at the end of the month. And then you can clearly see if the agency/freelancer is getting paid accordingly or if you made a bad deal.