if you're willing to put the computer together yourself, then yes! definitely worth it.
for ~$700 you could something like this...
nice aluminum case $44
seagate 250gb hard drive $86
asus mobo $80
eVGA 7600gt $179
fortron 450watt PSU $51
1gb 2X512 Gskill ram (ram prices change often.. so w/e is cheaper when you start buyin) $70
athlon 64 3000+ venice $111
total: $620.97 - $15mail in rebate = $605.97 + shipping.
so that would leave enough for you to buy a CRT monitor from a local store (buying crt monitors online is too expensive since they're so heavy you'll get killed in shipping.. just get a cheap one from a local store or a used one or something...)
you'd also have to get a mouse/keyboard/speakers, but those you can get for real cheap..
that should bring you to just about $700
thats a GREAT setup compared to the $300 budget.... you get a very nice video card and overall quality computer.
you also have to think about the OS....