I really feel that someone needs to break in here and contradict the "need...more....power...." refrain that's quite common on TB. 300W isn't "quiet jamming". 300W is playing a club with no feed to the PA. 300W is an SVT. You can do "quiet jamming" with a 50W amp, less if there's no drummer. I rehearse regularly with a hard rock band using a 150W, 1x12" combo, and it's not running at max volume.
If you're just starting out, focus on getting a decent, but not extravigant, bass, and *some kind* of amp that sounds OK while you practice. You're nor playing out for a little while. The club amp can wait.
Now, if you're shopping for a small practice amp and you come across a nice sounding used 250W combo that falls in your budget, it's always nice to have "headroom". But you shouldn't be spending more dollars to get more Watts at this point, IMHO.