the prices will vary depending on the EEG amplifier you choose, the electrodes, the cap, the softwares you want. Additionnaly, I guess the prices could be different depending on your "status", if you are academic, industrial, individual, whatever. You will have to contact each hardware provider to have a clear idea of the price for a complete hardware setup.
Here are the urls of the different hardware provider websites whom drivers are currently supported in OpenViBE :Mindmedia
for the NeXus32BBrain products
for the ScalpEEGTMSi
for the Porti32Brainclinics
for the Brainquiry QPETMicromed
for the IntraEEG is probably off topic for what you need
CTF/VSM MEG is probably off-topic for what you need.
I hope this helps