Prices and practical info as of August 2015. Completely different from any other places I have visited so far. Gateway to the Arctic area. If you want to start visiting Far North probably it is the best place to start.
Some basic hints - maybe will be helpful.
Flight - there are 2 lines flying to Longyearbyen - SAS (normal airline so you can take normal luggage with you - there are no free meals on board - and Norwegian, cheap airline - apart from the ticket itself you have to pay for the luggage as well.
Accommodation - the cheapest option is a camping site close to the airport (120 NOK if you have your own tent). More expensive are hostels - Coal Miners' Cabins (Nybyen) and Russian House (Russkij Dom) located more convenient in central Longyearbyen. The cheapest option start with 300 NOK per dormitory. In high season it is better to book well in advance.
Travel options - one day boat cruises - the cheapest (in fact the most convenient) are those organised by Polar Charter (Polargirl) - two main options are very interesting and covers quite a huge area around Longyearbyen.
Pyramiden trip goes to abandon Russian mining settlement going throught 2 National Parks on its way: Nordre Isfjorden National Park and Sassen–Bünsow Land National Park - full day trip.
Barentsburg trip goes through Isfjorden (Nordre Isfjorden National Park) to Barentsburg (active Russian mining settlement). Both trips are spectacular (especially with excellent weather) and highly recommended.
General warning - Svalbard archipelago is well know for its polar bear population. In fact there are more polar bear than people. All the trips outside Longyearbyen city limits should be equipped with a gun. In fact even the road from the airport is regarded as not fully safe.