Hello Hive account@smartesthinker! Nice to see you here.

Considering you used the brazil tag on your post, I'm assuming your fiat currency is BRL.

The cheaper and safer way I know to achieve this is the following:

Step 1: Open a mercadobitcoin.com.br account

This exchange is a bigger / older / most reliable on Brazil, I have an account there since 2014.

Step 2: Deposit your fiat currency:

Click on the deposit button, and you will be presented with the accounts where you can register and deposit the fiat currency.

It may take up to 3 days to confirm the deposit, but on all my experience, the money was released on the same day.

Step 3: Convert your Fiat Balance into LiteCoin

Litecoin is a faster and cheaper altcoin, which is supported by both MercadoBitcoin and Hive account@blocktrades

After changing to Litecoin on the dashboard, you may click the "Buy" and select how much, like o the following screenshot:

Step 4: Convert to Steem or SteemPower Using Hive account@blocktrades

Open the Hive account@blocktrades page: blocktrades.us, there you can select the origin and destination crypto currencies.

I Think that covers most of it. :)

Feel free to contact me if you need help doing that, if you decided to do so.