At the height of the season gulet hire will be expensive.Even cabin charter(i.e. sharing with other people)will not be cheap.(renting the whole boat would be astronomical!).The best bet would probably to wait until you are in Icmeler and go to the marina in Marmaris,there you will see a lot of boats with'for rent''2,3,4,5 day charters'etc advertised on boards hanging on the back of the boats.Have a chat with a few owners and see what they can offer you.
For a couple of days trip you would be able to go along the Bozburun peninsula maybe to Selimiye,which is lovely.
The girls are now at an age where they will probably enjoy showing off in their bikini's plus will love being able to swim and snorkel too-just make sure you have a few magazines,iPods etc for any moody moments

Thanx, for the info, will go to Marmaris and have a look..

Just a thought... the gulets that are normally available for 1 - 3 days are not usually the best boats.The best ones are all booked up for the whole week. You may be lucky but the cabins and food might not be up to the standard you can expect on the weekly boats.

Don't let it put you off gulets if you do get a sub standard one. As its you first time you might not even notice. We didn't when we did our first one 8 years ago. We still enjoyed it!