John,
I am not aware of any pre-existing products either, sans the Mianne lift section already mentioned. I documented my triumphs and pain in building a hinged lift bridge in my layout building thread, mostly on page 2.
Building the bridge itself is fairly simple... and can dress it up as much or as little as you want. The hard part for me was the unexpected fitting challenges and actually sourcing of the parts. Sometimes it was just a matter of finding the right search term to get the component I needed, other times it was learning the hard way where to put the hinge. Here's a list of my lessons learned (aka, things I wish I had known before starting):
1) For a swing-up lift up bridge, mount the hinges above the level of the track so the track affixed to the bridge swings up and clear of the track below - else the track will impinge on itself when the bridge is lifted. Setting the hinge point behind the track joint is another option, and ended-up being the way I went for aesthetics.
2) Cut the track using a thin cutting wheel, such as that on a dremel. Angled cuts, corresponding to how the bridge will swing, work best.
3) Ensure that the anchor points where the bridge is mounting & the track meets on both sides have no "give" - small variations in rail height are a big issue when running.
4) A hydraulic arm can be used to assist in lifting the bridge & ensure that it doesn't go back too far. Ensure you get one with a long enough arm to get you to 90 degree (depending on how you mount it) and enough force to lift your bridge. These are fairly cheap on amazon and generally sold for cabinets. You'll probably want to exchange the mounting screws they come with for more robust ones.
5) Furniture pins are great for ensuring the bridge lowers and sets into the exact same place every time without shifting laterally. Some kind of locking mechanism, like a trunk latch, is useful to ensure the bridge remains seated vertically. Both are available in big box hardware stores.
6) It is prudent to have a "bridge up" power cutoff mechanism in place so that trains don't run off a cliff when the bridge is open. You can use a cut-off on both sides - but should do it on the non-hinged side at a minimum. I ended-up using momentary lever switches (one for each main line) that are physically closed (thus closing the circuit) when the bridge is down. I also installed LEDs for each track so I have visual confirmation if power is off/on to the section leading to the bridge. I found both on ebay for a reasonable price.
-Dustin
