Here are the on premise pricing for Microsoft Dynamics GP another option you have is to run Dynamics GP in the cloud , the price would start from $178 per user.
Microsoft Dynamics GP 2013 Prices:
The Starter Pack (includes 3 full user licences): $5,000
The Extended Pack: $10,000
Full User: $3,000
Limited User: $600
Customization Pack: $6,000
Extended Human Resources and Payroll: $7,000