Pre Press Monitors

Hi.
We're a relatively small printers running Heidelberg Speed Masters 74 and 52. We're attracting more work now for art galleries, exhibitors and jobs where accurate reproduction is a pre requisite. Unfortunately our pre press doesn't seem up to the job as we're using standard Mac monitors which seem to vary from computer to computer. Can anyone recommend or have any suggestions regarding pre press print monitors. Suggestions ranging from entry level to high end with a rough budget of £2000 would be appreciated.
Thanks in advance of reply.
Jeremy.