This question is separated from theme of discussing units.
Probably everyone understand that all things have their own price. If you wish good thing you ought to pay for it. Free cheese is only inside of mousetrap.
But how to pay? That is a question I will speak below.
There is some ways to pay. If that are local payments, people use cash (may be credit/debet card, I don't know. People in my country use mostly cash, I think).
That about payments outside the country, there are some tested ways. One of them is planed in our site - cards.
Other one is in use by many other sites - international payments systems, one of which is called WebMoney (http://www.wmtransfer.com/).
Very easy to open an account on WebMoney. Very easy to sent money from one account to another. Probably in every country exist offices where is able to put your money on your account or to take your money from your account.
Why we have no account in WebMoney? Why we have no account in another payments system?
What to do if somebody haven't a plastic card, how to pay?
Next question is for what we will pay?
Offered scheme, to buy units, is one of worst of all.
Imagin, someone bought gold membership for... 200 years, he payed... much of credits. So what? Can he play good? No, if he need to buy any units, additional to his membership.
There was a TV programm about such games, which exist for they are produce more and more new items. And people, who wish to be a good player, must buy them because another way they will be beaten by others, who already bought such items.
I guess that three heroes, offered for credits, will not be last. After them will be else and else new credits-buy heroes/units/items.
I think that is very defective practice. And we must define, are we one of such games or not.
But if not for that, but for what to pay credits?
I can offer some ways.
1. Member's payments - silver/gold (already realized).
2. Limitation of current games. 2-3 games are free and 4-th and more if for some credits each. Player don't necessarily must be a silver/gold member to play many games if he pay for each of them.
3. Additional options, such as 'Find player' system, where you write a name and you will get open page with his account. May be 30 last battles of all players etc.
4. Ability to play speed games. Only for silver/gold members.
5. Toll maps (is like toll roads). To play on this map cost some credits.
Etc.
If you interested of site reputation, don't offer to buy units.
Everyone may have his own vision. Mine is above.
If total money are not enough, lets look at raising price.