The best value in a simple trailer for bikes is...Wal-Mart!
They carry the Sno-Bear line (same as Cdn Tire, Home Depot). $578 gets you a 4'X8' flat trailer with 12" wheels (much better than 8" or 10") and serviceable bearings. Wiring's all done, hardware is quality, and the trailer is articulating for all your dumping needs. Another $120 for a bike rail and wheel chock kit (you can order directly from Sno-Bear, or over the counter at the Cdn Tire parts section), and you're good to go. The trailer fits 2 bikes comfortably, 3 if you're creative, but you'll need to buy one wheel chock kit for each bike.
I've put roughly 9,000km's on mine in the last year and a half, and I get all kinds of compliments from folks, especially when I tell them what I paid. You might save $200 getting a used one, but a lot of them are real Frankensteins (snowblower tires mated to a buick regal differential, lighting system from a 1984 moped, capped off with some nasty looking plywood), and they're often those "wobblers" you see buzzing back and forth behind cars on the highway. Mine is very balanced, and virtually imperceptible on the back of the minivan. Or you could spend $5000 on spiffy enclosed trailer. Then I'll be your friend!
A trailer hitch will run you about $250, including install. So, you're looking at another $1,000 on top of bike purchase and safety gear. However, the trailer will hardly depreciate in value, your used bike will barely drop in value over a few years time, and the safety gear is a consumable that you'll replace piece by piece. Once you take the $5,000 plunge, it's not that expensive. Compared to golf or downhill skiing, owning a bike for trail riding or sand pits is a bargain. Or so I told my wife!