Salesforce Consultants and Contractors have 3 basic pricing models.
There are 3 payment structures you can use when hiring Salesforce Consultants. The right solution for your business depends on the project complexity, size of team needed to meet the objective, and ongoing support you require.
Fixed-Cost Project Pricing
The Partner will conduct a thorough discovery process and present a State of Work (SOW), which is a proposal outlining the specific deliverables, delivery timeline, and total cost of the project.
Provided the scope of the project doesn’t change, a fixed-price project can give you cost certainty. However, it’s harder to change the requirements of a fixed-price project, so they can be more limiting and is generally a more rigid commitment for customers.
Engaging a Salesforce Consulting Partner makes sense if you’ve identified a specific business need or new platform to implement and need several different types of Salesforce Experts to deliver the project.

Pros
For large scale projects, having a fixed cost helps create certainty around total spend since you will have the entire project scoped out from the start. This is a great strategic move for project planning. The Consulting Partner is also incentivized to work quickly (while still delivering quality). Big fixed-price projects can offer better value for money than hourly-rate projects because you’re guaranteeing the Partner income certainty.

Cons
You’ll need to pay a hefty deposit at kickoff- usually 50% of the total - which can be a substantial up-front payment. This is also a less flexible arrangement because if your scope of work or goals change at any point during the project, you are still tied to the Statement of Work (SOW) signed during kickoff.
For smaller companies with priorities that change quickly or strategy planning that takes place every Quarter - instead of planning for an entireYear - fixed-cost is a less flexible arrange and doesn't work as well.
Monthly Retainer
If you’re looking for someone who can support/maintain your Salesforce instance, or you have a series of projects that need to be completed over several months, a monthly retainer could be a great option.
Some companies might refer to this type of arrangement as ‘managed services’ and it’s essentially an outsourced alternative to hiring in-house Salesforce Experts. Consulting Partners and Independent Contractors both offer this type of monthly retainer structure.
The arrangement usually consists of a flat monthly fee for a set number of billable hours, which you can use for whatever tasks come up during the month. If you don’t use all your hours, you still pay the same fee but if you go over your allotted hours, you’ll be billed by the hour for the extra time.
You’ll usually be able to negotiate a discount off the service provider’s standard hourly rate because you are guaranteeing a block of hours for them to work each month, thus providing more stability.

Pros
You will have have more flexibility than with a fixed-cost project but you will still have on-call access to the Salesforce Experts you need, as you need them.
It also gives you some negotiating power when setting the monthly amount, so you may save money compared to paying by the hour.

Cons
You can waste quite a bit of money if you don’t use all your billable hours.
Customers want to make sure they know their work requirements before committing to a monthly retainer because many vendors have a 'use it or lose it' policy, meaning unused billable hours do not roll over to the next month.
Hourly Rates
With hourly rate projects - also known as Time and Materials - you pay for the Contractor's time only as it's used and simply pay at the end of each month.
FoundHQ provides a list of hourly rates for various types of Salesforce Consultants on this page and you can use those as a basis for estimating the costs of monthly retainers and fixed-cost projects.

Pros
This is the most flexible structure for customers.
You essentially have no upfront commitments, so you aren't locked into a certain type of project or amount of work. You will pay at the end of each month and are only responsible for the hours you actually used.

Cons
It is more difficult to predict what the full project cost will be until you see the invoice at the end of each month. This can sometimes be more expensive than committing to a monthly retainer because the Contractor has less income certainly. Typically, projects aren't scoped upfront but instead Contractors are identify projects and completing tasks on an ongoing basis.