What I do is:
1. Create a new Steam account (or use your main) that matches the country you are in or have legit payment options for (in my case, US). This acts as a payment account.
2. Use a VPN and choose the country you desire to make a Steam account for. Argentina and Russia seem to have the cheapest games. I have both as some games are cheaper in one country than the other and vice versa so you save a lot more by having two accounts.
3. On your main/payment account, add the account(s) you've just created as friends. Easiest way is using a Friend Code as newly created accounts have limited functionality.
4. Wait a while (about 3 days I believe) until Steam allows you to send a digital gift card to new accounts.
5. Log on to your main/payment account and go here
and click Send through Steam to purchase a gift card and select your new account. Choose any amount you desire to spend. Put in whatever you want under PERSONALIZE YOUR GIFT WITH A LITTLE NOTE. Click Continue and choose your preferred payment method (I use Paypal).
6. Once the gift card has been sent, log on to your new account and accept the gift. You will see the amount of money you've received under your account name on the top right in the account's local currency.
7. Buy something and use wallet balance as a payment method. DONE!
To determine which region to buy each game from, use this extension
on Chrome then go to the game's store page and click View on Steam Database. It will list the prices in all currencies.
The extension also allows you to purchase gift cards in any amount not predetermined by Steam.
Also note that using this method will allow you to share games across any of your accounts just fine so you can still game on your main account as usual but the account(s) you use gift cards to buy on will stay limited since the money comes from your main/payment account and doesn't count towards the $5 USD minimum requirement so it will still not let you do things such as adding friends and creating a group. I've heard that redeeming a physical gift card that matches the account's country works but I have yet to try it so cannot confirm that.
Oh and one more thing. Steam seems to actively detect VPNs, especially well known ones like Nord, Express and such. If detected, you'll be stuck in a captcha loop or it will just flat out say you are unable to make an account. There's really not much you can do but keep changing servers/IPs and hope that it works or find a lesser known VPN.
There are also a few sellers on ebay that sell custom made Steam accounts and gift codes if you want to go that route but figuring out which one to trust is another story.