It depends on how tolerant you are of spelling mistakes. In the example you give, I would certainly not consider 'echp' as a spelling mistake, because it's a non-existent word.
Could you please provide more real-world examples of acceptable spelling mistakes that you need, so we can provide a more useful help?
Marcus Green mentions using wildcards; but their use is very limited and can lead to accept all kind of incorrect answers as correct ones (as mentioned in the documentation).
If you are allowed and willing to add contributed plugins to your Moodle site, I can recommend my own Regular expression short answer plugin. But again we need more real-world examples from you.