Welcome aboard the RoadTrip America Forums!
And thanks for the compliment!
This post describes what I'd recommend as a relaxing, scenic, and interesting drive between Washington and Niagara Falls. If you're going from Toronto to NYC, then you might as well continue east from Toronto and complete a circuit of Lake Ontario. At its eastern end you'll cross back into the US in the
Thousand Islands region. If you then use NY-12 between Watertown and Utica, you'll be skirting the edge of the
Adirondacks and then be set up to run parallel to the old
Erie Canal, now known more prosaically as the
New York State Barge Canal. From Albany down to New York, The New York State Thruway offers the fastest route, but there is a toll (~ $5.35). The
Taconic State Parkway, on the east side of the Hudson River offers a more relaxed, and free, alternative. For the remainder of your trip you'll be on I-95 for the most part. This is the main transportation corridor for the east coast of the US, connecting the major cities of the northeast, so it will be heavily travelled and most of the sections that you'll be on are also toll roads (~ $19 between NYC and DC).
$3/gal gas must look pretty cheap. I was listening to a report this morning that petrol in the UK is approaching $10/gal! Overall, your budget looks reasonable, and by all means, bring some reserve.
AZBuck