Well, what does limited budget mean to you? In the audio world, reliability is something that comes with higher cost equipment, almost to a higher degree than sound quality. The most reliable bit bucket in the world might be the Aaton Cantar - the only recorder that is made to work in freezing cold and practically immune to humidity, rain etc.
I assume you only want two channels, and since you want digital in, that leaves three options in my book. The Marantz PMD661, the Sony D50, and the Tascam DR-100mkII. I don't know about the reliability of the last option, but the 661 and D50 are quite capable.