Check eBay. Or maybe just buy the NXT and motors if you already have a bunch of legos. Type your answer here...
The retail price for Lego Mindstorms currently is varying based on the size of the set. The average set costs anywhere from $500 to $800, depending on if it is new or used.
Lego mindstorms biotic is the best selling set ever made. It has sold over 1 million.
One may purchase a Lego train set online through Amazon, Ebay, Craigslist and Shop Lego. Other ways to purchase a Lego train set online is Cymax, and John Lewis.
look for Legos at garage sales.
wal-mart
Try bricklink.com. It's pretty much a Lego marketplace where you can get used set and parts.
You can probably purchase a Lego Star Wars 3 set at online websites such as Toys "R" Us, Walmart, Amazon, Target, or the official Lego website, for instance.
One can buy a Lego airplane set from the following online stores; Amazon, which sells airplane lego with very affordable prices ranging from 30 USD to 300 USD, Lego, Toys R us, and De Lupe also sell airplane lego online.
The Lego City Airport set can be bought online from any supplier who sells Lego kits. Certainly there are sellers on Amazon but it is also worth looking on Ebay in case there is a set there.
The best selling Lego set in 2014 is the Desert Skiff. It was created in 2012 and averages around $25 in the store and online.
There are many places online which you can by Lego pirates set. Amazon and eBay have lots of new and used Lego sets at competitive prices. On the high street any good toy store will stock a Lego pirates set.
You can purchase Legos for girls online at the Lego website. They have many different Lego sets for girls, such as the My First Lego Princess Set, The Summer Scene Set and the Poodles Little Palace, just to name a few.