They produced 8484 TR-250s, and they are very easy to find. For some reason, people think that because they are lower production, they are worth more, and I actually talked to a guy who was offering his for sale at $18,500. I had to explain to him that this price was about double of what TR-250s in very good condition usually go for.
I've owned a TR-250, and honestly, I'd rather have a TR-4. Less spark plugs to change, and fewer emission hoses to deal with. I'd also rather have SUs than Strombergs. Not to mention, that if you're missing some trim parts, they can be 250 only, and therefore cost three times as much to replace (like the $75 TR-250 emblem.)
Also, TR-250s and TR-5s all require tremendous clutch pedal effort. This was changed for the TR-6. Some people have done a common fix for this, but most haven't. My left knee would swell up from driving it in traffic.
Funny thing is that most TR-250s have had their nose stripes painted-over, so they look just like a TR-4. All TR-250s should have a light reflective silver transverse nose stripe.
It's a great car if you want something a little different, but as a first classic, I'd highly recommend the 4.