Easiest:
Travel to Manchester Airport. (There are good rail services from the East Midlands if you don't want to drive & pay for parking). Book your through flights with Olympic Airlines:
http://www.olympicairlines.com/
Sample times: Depart Manchester 2235 17/05. Arrive Paros 0930 18/05 (4 hours 30 minutes to change flights at Athens).
Depart Paros 1800 24/05. Arrive Manchester 2145 same day. (1 hour 5 minutes to change flights at Athens).
The fare for those flight comes to a total of �407.20
Cheaper:
Still use Olympic Airways between Athens and Paros but travel independently to Athens. (The only downside to this is that you might have to spend a night at Athens airport or book a room in an airport hotel). easyJet fly from Luton Airport. (Once again, there are good rail services from the East Midlands).
easyJet fares vary greatly but, if you can be flexible with your dates, you should be able to find some bargains. Here's a sample itinerary:
Fly from Luton at 1440 on 16/05. Arrive Athens 2025.
Overnight in Athens
Depart Athens 0855 on 17/05. Arrive Paros 0930.
Depart Paros 1835 on 23/05. Arrive Athens 1910.
Depart Athens 2055. Arrive Luton 2250. (NB: Because it's not a through booking, that might not give enough time for the connection. However, it's only an example; there are earlier flights from Paros).
Doing things that way, and ignoring the possible cost of overnight accommodation in Athens, would cost �136.09 for the easyJet flights and �90.70 for Olympic Airlines. So that's a total of �226.79
http://www.easyjet.com
You might be able to save a little money by taking the ferry from Piraeus to Paros but that means having to transfer from Athens airport to Pirae