It is essentially calculated as the interest rate times the outstanding principal amount of the debt. Interest expense on the income statement represents interest accrued during the period covered by the financial statements, and not the amount of interest paid over that period.
Even though my basement bathroom cost was around $3,700, you could probably do it for just under $2,000 if you really pushed the envelope, maybe even less. I'm not going to sugarcoat the project. From a time perspective it takes awhile if you're doing it by yourself.
Here are the best time-tested bathroom flooring options: Sheet vinyl flooring comes in a huge array of colors and patterns at a reasonable cost. You can find it at home improvement centers for $1 to $2 per square foot, and a competent DIYer can avoid the additional $1 to $3 per square foot for pro installation.