It can vary a whole lot when it comes to buying a new cube.
I mean, there are many preferences. Some people say that their modded, burnt, scrapped, broken in, lubed, re-stickered Rubiks cube can be as good as their Ling Yun, while there are some people who just simply say "ZHANCHI FTW period"
The cubes you get from the Rubiks Brand company are usually not that good, they are not smooth but not fast either, they have a huge amount of friction, the mechanism in it is not like a speedcube where a speedcube would have screws, springs and other mechanism like Dayan Torpedo's. But to be honest those speedcube mechanism is not needed when you're starting out, although of course it would be favored. I mean like, who doesn't like a fast smooth unpopable cube? But it is otherwise unnecessary if you're new to this.
Maybe a good lubricant or even some mods on a rubiks brand cube will do for now.
So, you say professional. Pro cube=good cube=smooth, fast (not too fast, but it can be changed) and has the ability to maybe cut some corners and do some "pro" features.
You would only get this type of cube online, UNLESS, of course, you are near some cube retailer shop. If you happen to be near a "pro" cube shop, you might wanna buy from there if they have you wanted cube because you don't need to pay shipping and often "in-store" products are cheaper than "online" products.
PROOF: It is said to be 14 bucks in the "China-magic-cube.com" but when my parents got their to buy it for me, it costed 10 dollars. 4 buck difference. 0.o
If you are not near a cube shop, then there are many websites to choose from. Take a look here: http://www.speedsolving.com/forum/showt ... Thread-New