Where are you planning on visiting? There are a couple of backpacker hostels in Stornoway (Heb Hostel & Fairhaven Hostel), the Gatliff trust has hostels at Rhenigadale (Harris), Berneray (North Uist) and Howmore (South Uist) and there is a SYHA run hostel at Kershader in Lewis. Unfortunately the hostel at Gearrannan has closed. There are also a number of campsites with varying levels of facilities and a large number of B&Bs, Guest Houses and Hotels spread through the islands.