With the exception of the Bedouin villages, all the restaurants, kiosks and service providers along the trail accept credit cards. The Bedouins haven't the infrastructure for that and will only take cash in shekels.
You can find ATM's in Mitzpe Ramon, Midreshet Sde Boker, and in-service stations. That said, these are small places and you should better withdraw your shekels in advance in bigger places such as Beer Sheva and Dimona.
Foreign Money and Exchange:
Foreign Currency is not particularly respected by locals and is rarely accepted.
You can change money in banks though you should expect significantly low rates. The post office is a better option yet frequent long lines are discouraging. Otherwise, very few exchange booths serve the Negev and like anywhere else in the world exchange rates tend to be lame or non-existent due to lack of competition.
To get your money's best value, exchange it in one of Israel's big cities.
Accommodation and food cost around 200 shekels per person per day. If you're camping and cooking for yourself this should go down to as little as 50.
Admission fees are on average 15 shekels per person per day.
Public transportation to or from the trail cost about 30 shekels.
Special activities' costs depend on the season and on the number of participants.
Costs for accommodation and food not directly on the trail are generally higher and differ from place to place.