As for average price (with diamond) depending on where you look the answer varies from $4k-$6k.
What I did to get the best bang for my buck is I bought a Kay Jewelers 'Santa Certificate' last year off eBay. I got a $3200 certificate for ~$700, helping me save $2500. Only potential downside is that these certificates are used to take $100 off every $300 spent, take a look at how they work to see if my idea works for you.
Other peice of advice from my experience is prices on rings and especially diamonds are negotiable. Check out blue nile and price a fee comparable diamonds to usual as a negotiation tool.
Good luck!