Depends on how long you stay. I can tell you the general fees for things:
Dining out usually costs on average 15-25 euros per meal (may include a glass of wine or dessert). 25-50 euros for nicer restaurants. And 250 euros for Michelin starred restaurants. Just stay away from tourist traps.. they make them more expensive than it's worth. You can go cheap and get a crepe or kebab off the street for 5 euros. Baquettes/Croissants cost 70 cents to 1.10 euro/each. Bottle water is about 3 euros. Oh and a cup of coffee french-style is around 5-6 euros. Glass of wine can be 4-8 euros/glass or 12-20 euros per bottle. Vodka in a club will cost 50 euros. Champagne in a club 100 euros and up depending on the brand.
To see the sites, average in about 7-15 euros per ticket for places like (most museums, Eiffel Tower, Bateau Mouche).
Metro tickets inside Paris one way cost 1.60 euros/ticket or 11.40 euros for 10 tickets. You can transfer with the same ticket, just so much that you stay inside the metro. If you think you will be hopping around to many neighborhoods, and will be using the metro a lot in a day, and you plan to stay a week or more, invest in a carte orange, which offers a weekly/monthly pass for unlimited rides, and could be cheaper than buying individual tickets.
You can also bike around with the Velib, which can be 1 euro for 1 hour and 2 euros for 7 hours..etc. Taxis don't take rides under 5 euros, and prices are not that cheap. I've gotten a taxi go across Paris for 25 euros. To/from airports to city is around 50 euros. And getting them on a Saturday night in front of a bar or club will be godsent. To order a taxi will cost you upfront 9 euros because they have to clock it where they are and the distance to it takes to get to you.
Nightlife and Entertainment can range from 4 euros / beer, 8-10 euros cocktail, 15-25 euros for cocktails in chic clubs, and 10-20 euros for cover at the door. The cabarets like the Moulin Rouge and the Lido can cost 100-150 euros a ticket (includes a bottle of champagne). And music clubs can be up to 10-50 euros depending on who is playing.
The theater can be cheap if you go to french indie acts 5-10 euros/ticket. If you go to more well known ones like at the Comedie Francaise it can be upwards to 50 euros/ticket. The Opera, if you are lucky to get a seat can be upwards to 100 euros/ticket. Bastille's Opera sells last minute seats for cheaper prices. But you have to be there on will call to see if there are any.
A good french haircut will get you from 90-120 euros without color. (if that's something you'd like to do)
Hammam, spas, and massages will be from 35-75 euros.
Clothing! Depends on your tastes. Cheap cheap clothes 5-10 euros off these racks off the street. Average is 30-50 euros per piece for better styles. Trendy styles can be 50-100 euros per piece. And for the Great brands.. average 500-1500 euros per piece. That's how they roll! :) Shoes, same deal.. you can get cheap shoes for under 10 euros. Expect the nice french/italian brands to be 500-1000 euros. Good sneakers are 65-100 euros.
What I would suggest is map out your plan before you get here, and check the sites, museums, restaurants you know and want to go to. Then you can use these prices as a general guide for your price range. For more precise prices on the attractions, they have websites on almost everything. But I would say, you can spend an average of 50-75 euros a day if you don't do/buy pricey things. There are ways to do it frugally, like looking for the free museum days, or walking (since Paris sites are almost clustered together) or eating at bistros in non-tourist places (they are cheaper and sometimes you get very great food).
And the safe thing is to have a backup Visa card/ Travelers checks.
Good Luck and safe travels!
Live in Paris!