Go-Today —
For independent travelers, couples, and private groups, Go-Today offers a large variety of reasonably-priced Europe vacation packages to Europe that include airfare. Prices quoted on their website are usually for week-long vacations (give or take), include round-trip airfare from New York and car rentals or rail passes. They offer a lot of Europe packages under $1500.
They also offer a variety of special interest Europe packages, including Food & Wine vacations, Culture & History, Honeymoon/Romance packages and more. They also offer a number of Castle & Villa vacations, including their Irish Castle Experience (enjoy unique accommodations in four historic Irish castles); Edinburgh & Scottish Castle Experience (an escorted tour); their Rome, Florence & Tuscan Villa vacation, and several others.
Note that most of their vacation packages our NOT all-inclusive escorted/guided tours. Although they do offer a few escorted Europe tours. While your flight, hotel, rail tickets, and a few other sightseeing activities are included, ground transfers from airport to hotel, train station to hotel, etc. are not.