Skiathos is lovely, great beaches, scenery and some lovely tavernas and Bars in the side streets in town.
If you want to dine on the front, or at the Windmill or Infinity Blue restaurants then you will pay a lot more.
Just behind the waterfront on the old harbour is a grill house, Its called Koziakas or "Ding dong man" as Michaelis is known locally. This is probably the cheapest and best grilled meat on the island and is next to the King & Queen pub.
At Sklitheri is the Sklitheri beach taverna,have lunch here looking over to Skopolos and you will be amazed by the colours of the water and the scenery - Land Sea and Air if only i could paint it !
Down at Koukounaries is Taverna Apostolis just past Bus Stop 23. Captain Michaelis is a star and you will leave here with unsteady feet, and and probably wake up feeling slightly the worse for wear
Take the bus if you can to save on car hire and petrol costs, remember taxis are shared but can be pricy anywhere in Greece.
Most of Mamma Mia was set over on Skopolos, but the opening scenes are Skiathos and Tsougria and the old harbour, and the view from the clock tower over the old harbour towards Tsougria.
Enjoy Skiathos, its a lovely Island, and you too could be like Keffaddict, Janbabe and me as returners or Boomerangers as we are more commonly known