How in the hell did you come up with 4 hours to complete a $1,000 to $10,000 job? Seriously are you insane? Do you have any idea how long a login system takes to implement, let alone a redesign?
If you don't have any skills in HTML, CSS, PHP, JS or WordPress/CMS, why are you equipped to estimate?
Hell, your website is about contractors quoting on work. Why don't you let the experts quote on a job? If you had the skills to quote, you would be doing this "four hour job" yourself.