I have a 2003 Ural tourist, and have owned it since 2009. Here's a few Ural buying tips:
Get a 750cc, which happened mid year in 2000. The castings and overall quality of the engine parts are significantly better than the older 650's.
If you want the cool triple drum brake, that ended mid year in 2003. The Brembo front disc does stop better though, but then your spare wheel won't fit on all 3 corners, so its a trade off.
2004 saw the introduction of the Herzog transmission gears, which are a huge improvement both in terms of strength and shift quality. 2004 also saw a beefier alternator. The 1998-2003 Urals alternator is nicknamed the "hand grenade". They blow up and take your timing gears with it (its gear driven from the timing gears under the front motor cover). Some blow, others don't. It's been attributed to crappy bearings and/or out of round gears. I got 22,000 miles on my original 'hand grenade' without failure. I think its a quality control issue. On a higher mileage Ural, the alternator is probably fine. On a low mileage one, it just may not have blown yet.
Post-2012 saw a bunch of little improvements, which are reported to increase reliability, but I can't chronicle them for you.
If you're looking for a 2000-2010-ish Ural on the east coast, nice ones go for around $5,000 and ones that need a little bit of work go for about $4000. $2500 buys you a total project.
If you won't use the 2 wheel drive, don't buy it. Its heavier and is more stuff to break. I have the one wheel drive, and regularly ride dirt roads and in snow up to about 8''. If you don't make terrible decisions you probably won't get stuck. Upgrade to 2wd for mudding and really deep snow.
The rumble seat mod is not viable for human use, although it looks col. There is no leg room in the trunk, so it only works for small to medium dogs - not humans. I'd imagine that putting too much weight back there would also unbalance the rig.
Speaking of balance, have you ever driven a sidecar rig? Its nothing like a motorcycle or a car. They turn right while accelerating, turn left while braking, and sidecar wheelie when making really hard turns towards the sidecar side. I think they're a blast and love mine... but I've taught some people how to pilot a sidecar and most decide that it isn't for them.
They're reliable if you go through everything and make sure they're built right. Some are, some aren't. Build quality is supposed to be better on newer bikes.
I've upgraded mine to the Herzog gears, completely re-wired the bike and used 'modern' charging system components, rebuilt the carbs with name brand parts, replaced the wheel bearings, swing arm bearings, and neck bearings. Its been perfectly reliable for me after the rebuild. If you're on this forum, you can easily keep one going.
With a passenger, mine with go ~70 mph flat out, but that's scary as hell: the motor is screaming, the chassis has so much slop that it's hard to maintain your line, and the drum brakes aren't up to the task.
Keep it below 60, and you'll be happy. It's NOT an interstate machine.
750's have the more 'square edged' valve covers. You'll also want the leading link fork, they greatly improve handling and reduce the acceleration/braking induced steering. Mine is a 750 with the leading link forks: