Don't know about taxis but it is quite a long way and prices are likely to be 'subject to negotiation'. I would suggest you have a look at Med Hotels transfer service on the following link. Just put Hammamet into the box and Hammamet Yasmine comes up as well. They seem to be very reliable and you don't need to have booked your hotel through them. http://www.medhotels.com/transfer/tr_viewprice_search.asp

Tried med hotels, but they don't do the hotel I am going too.
sequencedancer

I would think you can take the Medhotel transfer to the hotel nearest to your own hotel and from there on take a taxi to your hotel.

You can indeed do that or you can book it like that, smile sweetly at the driver and ask very nicely and he may even take you there - he dropped someone I know off at her appartment in Hammam Sousse. You would probably need to pick up the return transport at the nearest 'official' hotel, but it would still save a lot of money. When I needed to speak to the company in the UK recently (0870 220 2224) because I'd given them the wrong arrival time they were extremely helpful and even though my flight arrived nearly 3 hours late they were there waiting.

Have a look at this map to see where your hotel is in relation to others:

http://www.holidaymaps.de/afrika/tunesien/hammamet.html