I am the IT director for a call center located in Gilbert AZ. I currently have a team of 3 people including myself and this is what we all specialize in. We have a really strong team and we already built many related systems. Right now we are running on an HP DL580 5th Gen with quad quads and 64gb of ram that runs Elastix 2.4 running up to 70 consecutive lines on the G729 protocol. If your limited in bandwidth OR need more users I recommend G711 protocol.
I was looking at the requirements and it appears that you will need CRM with PBX integration as well. The PBX is actually fairly simple but the CRM with all the functionality requires more time to set up and configure.
If the CRM is a basic configuration then my quote will remain valid. If you require more such as tracking sales, webforms, module programming and reporting then it could be upwards of 10k. If you are looking to setup a fail-over system for high availability, please add 2 weeks and another $3500.
There are some unknown facets on this project, but based on what you listed this is our estimate. To discuss more details, please feel free to call Nick at (602) 386-6941. I will need to know what endpoints you plan to use, if you plan to have an internal network or an external whitelist?