The cost of hiring a Magento commerce partner depends on various factors like the customizations you need, the expertise you require and where the partner is based. For example, partners based in the United States are more expensive than those located on the other side of the globe.
Similarly, the more customization you need in terms of design and development, the higher will be your cost.
The cost also depends on the project scope, which determines how much time the partner will take to complete it.
It is best that you discuss with your potential partners about their rates and ensure they are in line with your budget before signing any agreement. To save money, consider hiring a Magento commerce agency such as Folio3 instead of an individual developer.