Joe,
I'll third the descriptions and kudo's for the 901. If neutrality, transparency, detail, harmonic integrity, speed, physical presence and endless extension at both ends interest you, this cartridge has all of it. It's alive yet non-fatiguing at the same time. With a solid table and a suitable arm the 901 is the cat's ass. Even a slightly crooked one like mine is jaw-dropping.
Be prepared to adjust VTF constantly. We hear differences with changes of .04g or less depending on the weather. Since January our typical VTF has dropped from 1.95g to 1.70, setting entirely by ear every time we listen. The easy way to do VTF on a Rega 250 is to add Twl's HIFI mod (get it from Tom) and then add my VTF-on-the-fly mod to that. If you have to move the counterweight to tune VTF you'll quickly tire of it, and you'll never get the most from a 901. Believe me, this is critical.
Also be prepared to adjust VTA, possibly for every record if you're a picky classical listener as we are. The magic of a 901 playing a large orchestra is indescribable, but you must set VTA perfectly to achieve it. Changes of .04mm (1/24th of a turn on the Expressimo VTA collar) make the difference between a flat presentation and a staggeringly 3-D one.
Finally, be prepared to have your records really clean. It may be partly due to our wood platter, but a properly set up 901 will play everything that's on a record, whether it belongs there or not.
I haven't heard any good arms except my modded OL Silver, so take the following FWIW. My current #1 dream arm would be a Kuzma Air Line, which "only" costs twice what my Teres 265 did. My dream pivoting arm for a 901 would be either a Schroeder Reference or a Triplanar. Any of these should be wonderful with a 901 or similar cartridges. A Basis Vector should play a 901 well but changing VTA on a Vector is a pain. I wouldn't put a 901 on a Graham myself, too many reports of loose bass for me to risk that kind of dough. Too bad, since in every other respect it's a wonderful choice. Maybe the new Graham Phantom?
BTW, what happened to "I'm on a budget"?! ;-)