Ok, i've found the answer that would suffice and look quite elegant. Here goes the required XPath string:
//table/tbody/tr/td[count(//table/thead/tr/th[.="$columnName"]/preceding-sibling::th)+1]
Put a name of the column instead of $columnName. This works well for me. There's no XSL or anything, just pure xpath string. How to apply it - it's another question.