Would it be fair to say overall that Lafayette is 30% cheaper to live in than Boulder?

An "entry-level" home in Lafayette is in the $200-250K range, while in Boulder your in the $350-$450K range. Lafayette will get you significantly more square footage. A larger, modern 3-5000sf+ home around Indian Peaks are typically in the $500-800K range (depending on location), while a similar modern home in Boulder starts at $700K and can easily cross the $1,500,000 mark. Louisville is between Boulder and Lafayette, both in location and price.