The prices may be the same, but what you get for your money is not the same. You will pay a premium for having a new construction home over an existing home. Why? Because it's new. It's similar to buying a car - you can pay about $45K for a brand new fully loaded Mercedes C350 or you can pay the same for an excellent condition, 4 year old, decent mileage S550. Some people will go for C350 while others will go the S550 - it's personal preference.
Regardless of which you may think you would rather go for, you should check out all your options. Have your Buyer's Agent get you all of the info on all new construction builders/communities in your price point in the areas you're interested in. Have them take you to see the model homes (some builders have models located in communities other than the ones you're interested in). Have your Buyer's Agent give you a list of all the current builder incentives, lot releases, etc. And have your Buyer's Agent give you the inside scoop on their and their clients' experiences with each builder in the area whether it be a local or nation builder with local presence.
As far as advantages of one versus the other...new homes are just that, new. The new smell, the lack of wear and tear, you getting to choose where everything goes (i.e. outlets, ceiling fans, HDMI points), you getting somewhat of a choice of the look and color of cabinets, etc. You also get the builder's warranty. The disadvantages are that you have to deal with all of the construction around you until they finish the community, the switch of the HOA from the builder to the future HOA management, the settling of the house (i.e. nail pops, dry wall tape, etc) and what some say to be lesser construction and attention to detail than "how they used to build them".
As for existing homes, the house has already settled and the previous owner(s) have more than likely addressed those issues. You may also find than an existing older home has been renovated with higher quality materials and looks better than a new home for the same price. For example...your new home has builders' "level 1" granite, decent cherry cabinets, their standard hardwood floors and the typical builder secondary bathrooms choice of materials. But the resale home has really expensive and awesome looking granite, top of the line cherry cabinets and high-end, wide plank hardwood floors and the secondary bathrooms have been renovated with top of the line contemporary vanities including granite and cabinets, awesome and expensive tile work (floor and walls), top of the line fixtures/faucet, etc.
There's more to it than just this, but this gives you an idea of some of the differences and just how much there really is to consider. If you would like to chat in more detail about the rest of the differences and what to consider, give me a call or email me anytime. I have worked with/represented many new construction home buyers in Loudoun County/NoVA and stay in constant contact with sales reps at all of the new (and future) new home communities and developments in the area.
Real Estate Consultant/REALTOR(r)