Should I score this horror film that has no budget?

Through a filmmaker friend I’ve been asked to score a feature length horror film. The fee is £150 + 1% of UK sales profits and needs to be done within 4-5 weeks. I’ve politely asked for double the amount(which I still think is ridiculously low) and they’ve refused.

Now considering I have never worked on a horror film before and the fee is basically not even worth my time at all, am I saying no to a good opportunity that might bring along more work in the future, or are they just taking advantage of young composers?

Should I take the hit financially and hope the film does well and brings in some money later on, or am I wasting my time?

Also, I don’t necessarily plan on making a career out of scoring horror films. Thoughts?