http://shop.ebay.com/i.html?_nkw=subway+rocket+mesa+boogie&_sacat=0&_dmpt=US_CSA_MC_Shirts&_odkw=subway+rocket&_osacat=0&bkBtn=&_trksid=p3286.m270.l1313
You can probably find a used one out there in your price range.
Some neat things about this amp:
1. It's loud. Really loud. If you're playing at home you'll likely not be able to turn the volume past 2. It could easily be used for small gigging and it will rock your balls off in the garage.
2. It has a great setting for metal. The distortion mode is really good for metal, nice and crunchy, with a lot of flexibility.
3. It has a great setting for blues. The clean mode really complements twangy guitars.
It has a floor pedal to control settings on the fly.
I managed to score one from a friend and it's a perfect match for my Schecter Hellraiser - a guitar that handles both metal and blues with a lot of character.
You can expand this thing later by plugging the amp portion into a cab -- you don't have to use the speaker build in.
It feels to me like a good introductory tube amp.
THAT BEING SAID:
You should also consider a POD X3 Live or similar POD. PODs are amp / cab simulators are they are REALLY SWEET for beginners. I really should write up a separate post. With a POD you can simulate different kinds of effects, pedals, cabs, amps, and even microphone placement. They are great for learning how everything works and experimenting with different kinds of tones before you invest in an amp. You can also easily get a pod for your price range.
The POD is great for home practice because you get the full tone just plugging your headphones in...or you can use computer speakers. Or you can output it to a DAW or an amp...so you can expand down the road.
You can also download and share the tones you create and there are several people playing death metal demos on youtube using a pod and then sharing the configuration they use so you can emulate their sound.
It's a great tool to learn how to organize your effects chain if you get into pedals and effects later on, too.
The POD comes with a thick manual that describes which amps and cabs the simulators are simulating, so if you like a particular sound you can then go out and try it for real... The "Dual Treadplate" simulator -- for example -- is a Mesa Boogie Dual Rectifier simulator.