I don't think there is a specific site to find flights to Prauge, but if you look last minute there is a good chance you could find something cheap. I use
www.expedia.com and www.orbitz.com will both help you find the cheapest flight to London.
The cheapest flights are typically found on Tuesdays and Wednesdays.
The internet can help you find the cheapest London rates. I found offers of London flights from $49 at LowFare.com, and $289 roundtrip at WholesaleTraveler.com. There are a ton of websites dedicated to finding the lowest fairs for airlines. I would try either Bing.com or Hotwire.com for the best prices.
On the web at the Direct Flights web site.
Travelocity
Check out www.ryanair.com or www.easyjet.com
The airline that offers the cheapest flights to Cook Islands is Air New Zealand. You can find prices for flights to Cook Islands at the websites Orbitz and Skyscanner.
The cheapest day of the week to book flights is typically on a Tuesday. Airlines often release their discounted fares on this day, making it a good time to find deals on flights.
One can find the cheapest flights from New York to Indianapolis by looking up online or by contacting an agent in the nearest travel agency to one's location.
The US airlines that offer the cheapest flights to Italy include Air France and Alitalia. You can find more deals or book these flights from the SkyScanner and Trip Advisor websites.
FlightHub is your best bet for finding cheap flights. Always keep in mind that the cheapest day for flying is Wednesday, and ordering your ticket about 3 weeks in advance gets you the best possible offer.
There are a number of websites that will try and find one the cheapest flights to Venezuela. These include Trip Advisor, Expedia, Sky Scanner and Cheap Flights.