There are also lots of ways to economize if you're staying in a city long-term and are creative. As noted, $80/month gets you unlimited local transport in Paris (as far as Fountainbleu, Vaux le Comte, Chantilly, Versailles, Malmaison, etc.). Also as noted, the $100 "Vaudoise" pass from Swiss Rail gets you three days on unlimited and 4 days of 1/2 price travel, including the Lake Geneva ferries and the special tourist view trains. While my wife was working, I'd take the train every morning for a day of hiking and sightseeing in Gstaad, Gruyere, Les Diablerets, Vevey (the Chaplin museum), Montreau, Leysin, Portes de Soleil, etc.
Restaurant meals tend to be less expensive in Europe than in the U.S....I'd get a 3 course fixed price lunch including wine, tip and taxes for about $20 nearly everywhere in Paris or Vienna. And you can have dinner in a very nice restaurant in Paris (say a "baby bistro") for $50 to $100 a couple all in. Cooking is very economical and take out (breads, cheeses, roast chicken, cooked meats, Asian) is quite reasonable.
Many museums in Spain and Portugal have senior rates at 1/2 price or less (though that's rarer in France, Switzlerland, or Austria). But memberships may be worthwhile. In Paris, we have a Louvre membership (since DW draws at the Louvre 5 days a week) which was well worth $140 for two, including the ability to skip the entry lines and reciprocity with a number of other museums. Our Barnes Museum membership (Philadephia), which also costs about $140 for 2, gets us into the Jeu de Paume and the Musée D'Orsay in Paris and our Whitney membership (also about $140) gets us into modern art museums all over Europe and the U.S. (including the Phillips in DC, the Art Institute in Chicago, etc.). When we were staying in Vienna we joined the Belevedere for about the same price, though you can buy 365 day entry for even less. And, our membership in the Arts Club of DC (or the equivalent memberships at Clubs in other cities) gets us resciprocal priveleges with private clubs all over the world (including London, Paris, Vienna, etc.)
Some things can be quite expensive in Europe! 3* Michelin restaurants are upwards of $500/meal (though sometimes you can do better), car rentals can be pricey (but not always), etc., etc. But theater, symphony and opera tickets are usually less expensive then here (and in Vienna, include standing room on the main floor of the opera for about $20 each!). As we said, housing is the big cost (and perhaps the most important factor in an enjoyable stay). After that it's fairly easy to economizd!