What costs I can expect when designing A LAN? How can I keep costs to a minimum?

A LAN will have a server, a switch, cabling and network cards. You may also have print servers (recommended) or you can share printers. Above that, you will have some type of security mechanisms. This can be login authentication, etc. If the LAN will connect to the Internet, you will need to have a router. As for costs for these components, they vary greatly depending on functionality, warranty, maintenance charges, etc. You will need to do a proper ROI calculation in order to determine overall costs. A TCO calculation will help you determine the costs over time. Check out the article "ROI/TCO fruit salad" for ideas on selecting your equipment. The most important thing to remember is you get what you pay for. If you go cheap, you can not always expect business level support or the same longevity in equipment. Check the equipment's mean time before failure and mean time to repair. Feel free to write back if you have any other questions.