1511 has built a near real field for the last several years for our Preship Rally, and more recently for the Monroe County Fair, for somewhat similar reasons.
You can see some photos here:
2010 Monroe County Fair
2011 Rally
2010 Rally
It is very similar to the scrimmage fields and warehouse build season fields that many teams build, as it is mostly built out of wood, plus lexan drivers stations & conduit siderails.
In the past one of our mentors has written an FMS, and we have also used/modified the FMS lite to work for us.
However, for the offseason event that we run, we generally use the NASA field (though have borrowed a FIRST field in the past).
Ruckus 2010
Ruckus 2009
This can be a very costly endeavor either way. Borrowing the NASA or FIRST field often costs around $2K, plus you need to be able to provide insurance (sometimes can be done via the school or sponsor policies). To build a field similar to the one that I have shown depends upon the year, but its probably close to $2K plus for the outside structure, and another $2K for the internals (ramps, goals, structures, etc)... and this assumes you have borrowed carpet. Plus you also need to buy fiberboard to lay under the carpet so you do not damage the gym floors or other surfaces. All told over 3 years its probably close to $10K investment.
This doesn't count the truck rentals or trailer that you will need to be able to transport all of this. We spent another $3K on a trailer and have access to a couple of pickup trucks that we can sometimes use.
The official field electronics is a whole different story. Even with all the events we have run, we have never seen a real need for the full blown system. And with my limited knowledge some of the "secret" behind it, my guess is that it is likely that FIRST is constantly upgrading and making improvements (like any engineering company) so they second they release something to the public, they not only have to support it, but they have to provide upgrades. That's likely more than their staff is able to handle. A clever group of SW & Electrical folks could probably fairly easily create an electronics system that would replace the FMS system and do a reasonably good job for demos & scrimmages (as we have in the past).
I'm sure its not exactly the answer you were looking for, but if you want to know more about the field 1511 created, you can PM me or submit to their
contact form.