With a budget of $268,000, Monty Python and the Holy Grail was one of the first I thought of.
Roger Corman made some decent films with very low budgets, and some crappy ones. “The House of Usher” was made for $200,000. The budget for the original “Little Shop of Horrors” was reportedly $30,000. Most of his films were made for under $1 million.
Roger Corman is well regarded today as a director and a producer. He had serious skills in managing a shoot, and had a degree in industrial engineering which likely helped him keep to low budgets and efficient shooting.
As I’ve grown older, and have had to wrestle with making a production on almost no budget myself, I’ve come to appreciate more the efforts of guys like Roger Corman and Bert I. Gordon and even Ed Wood, trying to eke out the most from their minuscule budgets, and the clever ways they managed this.
But I’d hesitate to call Wood’s or Gordon’s work “good”. Corman actually managed to produce a few things that were definitely “Good” or even better, but the bulk of his stuff wasn’t really. I include his EDgar Allan Poe films from the 1960s among the “not really good” category. I love them, and they feature work by some impressive talents (Vincent Price, of course, Boris Karloff, Peter Lorre, Basil Rathbone, Patrick Magee, Jack Nicholson, etc.; screenwriters Charles Beaumont, Richard Matheson), but, evaluated honestly, not really all that great.
I can’t speak for anyone else, but for me, there’s something about the combination of cute puppets and over-the-top (way, way over-the-top) debauchery that is, somehow, funny. The same movie with humans wouldn’t work at all.
That said, I’ve never felt the need to see it a second time. And it’s completely different from the Lord of the Rings films that most people know Peter Jackson for.
I think I’d describe his movies as “better than they had any right to be”, given the constraints under which he made them. As you say, few if any rose to the level of ‘great’ or even ‘very good’, but they pretty much stand above similar films made for similar budgets on similar time frames.
Corman got as much work as he did because he could reliably bring a cheap movie in on time and budget, and produce something a little better than the average schlock playing in that market.