One thing to keep in mind is that even presently affordable titles could see price spikes if backwards compatibility expands to other Xbox games. Worth mentioning in your next Xbox video- I know there’ll of course be one. Speaking of which, the following are some that aren’t (yet) valuable, but from my own collecting experiences are easily very uncommon to rare, and worth mentioning for that alone. Several are also hidden gems:
Volvo: Drive for Life- not at all expensive, but surprisingly uncommon. I’ve never stopped collecting for the Xbox, and this is one of the few titles that I’ve never actually seen in the wild. Basically an advertisement as much as it is a game, it still manages to be fun. This also has become a great period piece. It may not have ever actually been sold at retail, but a fair number of copies were given to Volvo dealers. This is by far the most affordable rare Xbox game- even now in November of 2017 new copies can still be had on Ebay for around five dollars. Here’s a good article on it from the Times:
...that article is itself a great time capsule, too- and not the mistaken use of “cartridges”.
Lucasarts Xbox Experience Vol. 1 (there never was a second Volume)- mostly just rare, and unlikely to be found in the wild. One of the only titles I’ve never seen in the wild. Often overlooked by collectors.
America’s Army: Rise of a Soldier: the Official U.S. Army game, and a surprisingly good FPS. Came out in 2005 to little notice. At least around here I haven’t seen too many copies in the wild. This is also on the 360, but is still worth getting on the Xbox. I personally greatly enjoyed this title due to the realism and inclusion of some RPG elements for player character development. I haven’t actually played this in over a decade, but will soon to see how it’s aged.
Shadow of Memories: Apparently a European exclusive. Never seen it Stateside. Had to order my copy online. Have yet to get around to playing it.
Roadkill: Great vehicular combat game. When I came across a copy two years ago in the wild it made me stop and go “now here’s a game I didn’t know about”, which hadn’t happened in a good while before that. Also on PS2, but the Xbox graphics are much better.
F1 2001: Probably the earliest “rare” Xbox game. I’ve only seen it once in the wild, at least knowingly- any other times I might have just glanced by it without even thinking it worth getting.