I think that making people pay extra to play the class they want is rather.... odd, especially since this is a video game where people are meant to have fun. Such a system is much too controlling and really has no place in Nord Invasion. Might as well make every class other than Commando cost 1000000 ranged and melee xp since there aren't enough commandos :/ (extreme exaggeration, but I think it gets across my point).
Alright, so "balancing" hero classes by changing how much they cost in order to get players to play the less used hero classes is a very controlling and ridiculous system to put in place. This would be very detrimental for new players that don't have much gold, as they will see that the class they want costs much more than the ones they don't. This would pretty much FORCE players to play the classes they can afford, while the rich players can play as whatever they want. Ah, here comes a hypothetical anecdote!
Imagine being completely new to the game. You are working and grinding and playing, always slashing and having a great time with your buddies. You finally hit level 52 and manage to save up 750k gold, a HUGE achievement. Now, you go to get that sexy Zweihander hero class you have wanted ever since you heard of it. Nope, it costs 2 million gold. However, there is an amazing (terrible) ROYAL GUARD position that you can get for 500k! Wow! Well, guess what, regardless of the stats you are still going to do in game what you want to do or have a rotten time. If you have 15 shielding (way more than anything should ever have ever) and hate shielding, and have only 7 power strike and 200 2h WPF, you are still going to slash because that is what you like doing or you are going to shield and have a miserable time, something people don't like to have in their games. Making it so that people cannot have the stats to go with their play style unless they pay extra fees is kind of like putting extra tax on people that like bananas because too many people like bananas. It is ridiculous and is liable to get a lot of banana lovers angry.
People are getting classes based on their playstyle, and that is great and makes the game fun. People that like to slash as Commando get Zweihander, people that like to shield as Commando (and Winter, because he is an idiot) get Royal Guard. That makes sense. Making people that slash play as Royal Guard because they cannot afford Zweihander? Not so much.
Of course, you could just say that if players aren't forced to buy the cheaper class and could just save up for the one they want. That would be a fair counter argument. Still, remember that banana thing
Oh, right, last thing. If it ain't broken don't fix it. Right now classes that are unpopular are getting adjusted so that the classes themselves are balanced, rather than making the good ones cost more, which is complete bogus. Just look at
Duelist Legionnaire! Before there were very few, but now it seems a very popular class due to a minor adjustment making it a much more balanced class.