If at all possible buy something you can examine before you purchase it. I bought my Toyo 45G on eBay for a very good price after asking the seller to verify the condition was as listed. Turned out that most of the controls on the rear standard were stripped or otherwise damaged. He did say the bellows were no good, which turned out to be true, and I replaced it with a cheap one from a Chinese seller on eBay (see "$69 eBay Bellows" thread). I have another rear standard coming from another eBay seller, if it is as represented and verified by the seller, I will have a fully operational camera for about what I could have bought one for in the first place. In other words, I saved nothing by buying what seemed like a bargain from eBay.

I would go with the monorail suggestion, for best price and versatility. I would only suggest a field camera if portability is the most important thing on your agenda. Even then, I would suggest getting a "freighter" backpacking frame and carry your monorail in a hard case with that. You can save a lot of weight by going with compact light weight lens instead of the heavy studio type lenses; the trade off is usually the maximum f/stop and a bit of coverage.

And speaking of coverage, don't buy into the your need an insane amount of it. I have found that my 135 Optar from my Crown Graphic, a lens that is reputed to have no coverage at all, will at f/16 cover the maximum standard bellows movement on my 45G. I doubt that it would cover the movements I would have with a bag bellows. In other words, the movements are limited by the bellows, not the lens. And that lens weighs something like 6-8oz.

As to set up time: I carry my 45G knocked down in a pelican type hard case, the tripod in a bag, and a shoulder bag with film holders, lightmeter, etc. Setup goes like this: set up tripod, mount rail to tripod (I leave the rail base on the tripod as it acts as a quick release that way), mount front standard to rail, mount rear standard to rail, install bellows. That takes like 2 minutes. Since you are going to take at least 10 minutes to set the shot, that is not a problem at all. At home, I just leave the camera set up with a plastic bag over it as a dust cover, so ther is no set up time for the camera.

As to brand, none of these cameras were junk (previous owners could have changed that) and they were intended for professional use and abuse, so pick the one that has the features you like. I picked the Toyo 45G, because I hope someday to get a 5x7 rear standard and bellows for it, so the modular format feature was important, and the 45G was the cheapest (used) camera with that feature. Note however that no camera with that feature is going to win the light weight and compactness contest.

The above is written from the viewpoint of someone new to monorail cameras; but not to 4x5 as I have had a Super Technika, and currently a Crown Graphic http://www.graywolfphoto.com/presscameras/index.html.