If you are looking for a big balcony but a good price then look at going with Costa or if you can spend some money then perhaps Royal Caribbean. Many ships these days the price goes up according to the size of the balcony even though the size of the room does not move up. Or if you want something informal try Ocean Village as they have different types of balconies - some friends of ours have just come back and they have one which had a cut out so it was a sort of balcony.
NCL are reasonable, staterooms are nice, travelled three times with them and ejoyed each trip. Going again to the Med with them and have booked balcony, SAY NO MOR.
I've found that some of the MSC ships have reasonably priced balconies, On the Lirica and Opera (their medium sized ships) you have a choice of cat 10 that is a room with a balcony or 11 that is a suite with a balcony. Not so sure about their 2 newest bigger ships. Try looking at a few websites - they usually give info on cabin sizes and layout.
Try Costa Fortuna Sailing from Barcelona, Some very good deals around at the moment.