PR5 website worth - thinking of selling

i know people always say your website is worth how much someone is willing to pay for it.

I have a site which is 4 years old, PR5 and on first page of google for prime keywords (mobile industry) with revenue of around 100K a year based on only adsense and couple of other ads. Lots of room for improvment and optimization as far as selling ad space is concerned.

Would asking $500,000 be reasonable? This would include the db of email,phone, age, city, country, gender of around 150,000 registered users.