Helps with planning a trip in winter break

[polygonal]

I have to admit that I haven't done any planning, but just wonder about the possibility...

I have about 3-4 weeks after Christmas and simply want to get myself moving (for experience and also for health reason that I don't want to stay home). I'm a poor student so this won't be a grand trip; and I'm very likely be alone (a girl that I'm). Starting from Maryland, I've been to much of the east coast, so I'm thinking going west - by car or by Amtrak.

I'm really in need for some suggestions: I don't have set goals (well I do but those are near the west coast so probably not for this time) but do want to see more of America. I haven't done (or planned) any trip in the US before, so I would appreciate some realistic estimation - how much should I expect to spend? It is safe for me to go around alone? How far can I realistically go with considerations on costs as well as experience (don't want to just drive through a state and say I was there) ? Suggestions as to which direction to go - straight west, southwest, northwest (I've been on a trip to the Niagara Fall before)?

Sorry if this is somewhat vague; I don't have any set plan at all, so I also would not mind if I do two or three smaller trips or even not spending the entire 3-4 weeks in traveling. I just want to gather some idea and start planning.

Thanks in advance!

(I've traveled alone before, so this won't be my first; I spent under 2800 euro grand total for a 3-month summer in Europe - although not traveling on most weekdays while I was there since I have day-time semi-job; went for a 6 days trip in Italy while I was in Europe for around 160 euro; also once slept on night train seats for 3 nights in a row, so budget or extreme budget traveling won't be my first either).