Ooops ... you're likely to be in trouble. At least officially, you are not allowed to enter the Republic of Cyprus (the southern part) coming from Ercan.
Technically, you can take a taxi from Ercan to the demarkation line, then walk trough the demilitarized zone controlled by UN and enter the Republic of Cyprus (if they let you in, but they are not supposed to ...). Then you could hail a taxi to a hotel or to Paphos (which is a long distance and likely to be expensive). Obviously, you take the same (high) risk of not being let through on the way back.
Bottom line: Not a good idea to fly to Ercan if your final destination is Paphos.
I'd strongly recommend to travel via LCA (and thus not via IST).