The easiest border crossing between Israel and Jordan is the Wadi Araba Crossing near Eilat and Aqaba. If you're taking the bus from Jerusaelm have it drop you off on the side of the road before you arrive in Eilat. You can walk from there. This will save you a taxi ride.

Israel is probably one of the more expensive countries you'll visit. You can save money on food by getting felafel sandwiches at the streetside stands and bagels in the cafes, but eventually you'll get tired of this. If you're in Israel for any length of time and want to save money, make sure your accommodation comes equipped with a kitchen. Most hostels do. Then do your shopping at the local markets. It's cheap, fresh, and a lot of traditional foods. It's not just going to save you money, but it'll give you an authentic experience as well.