I would suggest you go there in Autumn, why?
In 2003 i went to Paris( SUMMER) , if you still can remember, during that time in Paris the temperature rised up to 40 degree celsius, is the hottest temperature in the last 100 years, during that time lots of people died.
Paris transportations are very expensive, just like Subway each trip is 1 euro, bus also very expensive, but taxi is the most expensive. But the worst is in paris, the bus, subway they dont have Air conditioner!!!! When i took the bus , because the bus is no air con, so they just open the window, however although the bus have plenty of seats, i dont want to sit because the seat are crazy hot, and the handrils are metal, so they also very hot,i think you wont like hot weather isn't it? So i wont suggest you go to Paris in summer. But if you still want to go to In summer, is not a big deal. Yes , maybe the air tickets are expensive, but you can book it before you travel. Air France they have promotions right now, each person is like $4280. So you can book it now. Hotel just depends on what area. When i went to Paris, i lived in Holiday Inn Express, per night was $880 ( include breakfast) , also is pretty convenient, there is a subway station next to the hotel.
However Autumn is much more better , the temperature is around 15-20 degrees celsius( some times may be over) , but is pretty cool. So when you travel on the bus, subway, you will feel much more better.
In the other hand, i suggest you go to learn some french before you go, because not to many people can speak english. When i just took the subway and buy the ticket, the seller can not speak english, so what he can do is guessing. So in this case you should know
1) Je voudrais achter ........( I would like to have ......) achter pronunciation= arsh day
when you know how to speak , will be very convenient.
p.s Air France promotion will be finished on March 25, so if you want to go, please book it immediately, if not will be expensive
http://www.airfrance.com/double6/home.nsf/(LookupPublishedWeb)/HK-PublishedmarketHKen?OpenDocument
參考: Travel experience, Air france , my stupid opinions