what do you mean by "is still close enough to the original"... well, if I would to make it into 3D (but almost the same)...would be it close to original? what do you think?
And pls. how (in your opinion) could cost licence for such a game?
First, IANALADNEPOOTV (I Am Not A Lawyer And Do Not Even Play One On TV.)
Well, there are two possible infringements: trademark and copyright.
Trademark infringement would be if the game you create infringes on legally-filed marks. In this case, the key test (since were obviously past the other tests like the "similar goods" test) is "would an average consumer (not a fanboy/gamer totally plugged into the scene) confuse the two products, infringer vs. infringee?" If you create a game, and use a trademarked items like "Green Thomas: The Green Woods" and simply change them a little, like to "Green Thomas: The Green Woods' Trees", then I'd say there is a very valid case of infringement should the infringee want to pursue it. If the font is the same, and other details are the same, then you are really shoving yourself further into a hole. The other test is essentially if there is intent to benefit.
Copyright is similar. There is a similar "confusion" test: would an average person recognize the alleged copy as having been appropriated from the copyrighted work"? Another approach used in parallel is that the judge(s) will evaluate the work as a whole, "a.k.a. substantive similarity". You may replace a plumber with an electrician, and lobsters with shellfish, and you save your electrician's license instead of a peachy princess, but if the electrician jumps onto and knocks offscreen the aggressive shellfish, while attempting to save the his/her license, you have infringed on Mario Bros. The problem is obvious: subjectivity. When is the sum of all the elements in a work conceptually similar to another work? Well, it depends usually on which side has more cash for better and longer-lasting lawyering...
The basic thing is, try not to actively get yourself into a grey area, esp. if the infringee has a history of being litigious, ex:Tim Langdell.
As for licensing costs, there is no rule-of-thumb. It's whatever the licensor thinks they can grab from the licensee, plus the added factor of if the licensor wants the licensee to be successful or not.