YOu say "international," but does that mean europe, asia, africa or where? Never been on a guided tour, but tend to agree with Erik911. You are likely to end up with the "If it's Tuesday, this must be Belgium," experience. It can be more relaxing to spend a week or more in a single city (Paris? Rome?), and most tours allow only a day or 2 in any city - and you miss the countryside entirely. If you were by yourself in Paris, and wanted to visit the Champagne region, you could just hop on a train. On an organized tour, you would never see Vaux Le Vicomte or get to sample a gay restaurant. Unless one has a terminal illness, there would be many more years to come to visit other locations. Like Dash said, you can always get a local tour.
When I was your age, I went to Europe for two months by myself and had a great time - ended up not seeping alone in most major cities and some smaller ones - that might not be as as likely or possible today. When I wanted to go to a new place, I just hopped on a train.
I would not consider an organized tour (unless it were a gay one) in europe. Maybe other parts of the world, like asia or africa. In europe, it helps if you have a smattering of some major languages, but is not really necessary to travel today.
Saving money - investigate the Rick Steves books - recommens inexpensive lodgings. In summer, in europe, it is possible in some places to overnight in monasteries or university dorms (the cheapest) . Also, there is thte "Let's Go" series of guidebooks, geared to the budget student traveller, If you insist on being on a tour (and don't want to be bored out of your mind by your companion travelers) try a gay tour. It is almost guaranteed that you will meet some interesting travel companions. These tours can be more expensive.
You might try Out Adventures: http://www.out-adventures.com (which has periodic ads on RJ), or Hanns Ebenstein Travel: www.hetravel.com
The tour site at http://cruisingwithpride.com/all_gay_tours.html
lists a number of gay tour companies.
You might consider a bike tour in a limited area.
I had a great time once on a Hanns Ebenstein river rafting trip in the Grand Canyon