So, since I don't have Credit Card I can't directly purchase though Steam. So i saw the billing page (https://billing.spiralknights.com/billing/catalog/choose.jspx) that let's me purchase though "Pay by Cash" which supports "Dineromail" and that Dineromail supports "Pagofacil / Rapipago" (Something that doesn't come really to the thread, lol)
I said i'm using Steam, so I don't know if i'll be able to purchase though the Spiral Knights site instead of using Steam. I am able to purchase though the site even though i'm using a Steam account?
Once you migrate your account to Steam, all purchases must be made using your Steam wallet. So your answer is no, you may not purchase from the Spiral Knights store page. All purchases must be made through Steam.