Sohtnax,
No one appears to have answered your ballpark pricing request, so here goes.
I have a customer with a similar situation to yours, but a little farther along the path. They started with a Norstar, grew to about 140 phones. They wanted to postpone the cost of a PBX purchase, so we networked a second Norstar. They grew to 250 phones and were expanding again, so they went to a Nortel Meridian Option 11C, which uses different phones. (The SL100 is an old Meridian system.) Current Meridian systems are the Option 11C, 51C, 61C and 81C. The Option 11C is a wall mount PBX that grows to 5 Cabinets and 900 Ports. The larger systems use the same phones as the 11C. With PBXs I would stay with refurbished to keep the price reasonable. You should be able to get a system with 200 phones installed for about $100,000. The cost of networking another norstar with say 100 phones on it would probably cost you about $50,000.
The Definity G3 is the comparable Avaya product. Look to pay about twice the price of a comparable Meridian System. Then, be ready for Avaya to jerk you around for transfering ownership of the switch. Upgrades are another area where they rake you over the coals. I once bought a refurbished Octel voicemail (an Avaya product) for $10,000. The unit retailed for about $75,000. Avaya wanted $40,000 to transfer ownership. Nortel charges a few hundred dollars for the same transfer and their upgrades are reasonable.
I would stay away from Intertel. Nortel and Avaya own 80% of the PBX market for a reason. As far as pricing, the last Intertel quote I saw was quite a while ago. It was $30,000 for a system with 30 phones. I don't know if that translates to $200K for a system with 200 phones or not. I was an Intertel dealer back in the early 90s. I got tired of their poor quality.
Pricing can vary based on what part of the country you are in.
Hope this helps. If you have specific questions about the above info, feel free to email me.
Steve
phonebiz@bellsouth.net