I’ve noticed that Daijisen lists 前 as kanji for さき together with the expected 先. However all compounds at the end of the article include only 先, and I don’t think I’ve ever seen 前 with furigana さき. EDICT only lists it as nanori. Is it actually used?
前 pronounced as さき was not very rare in the past, but in today's standardized Japanese, it's almost never used. You can usually expect 前 comes with furigana if it's intended to be read さき. You can still see it in some proper nouns (e.g., 松前町).