Here it would have to be at a thrift shop or consignment store or something like that, perhaps ebay, the only other option would be to wait and save

In the US that's not possible if you buy it new. I'd have to go used/thrift it or go to a cheaper store like Ross where you can piecemeal that sort of thing

If you know your sizes, I'd go to eBay or an equivalent and try and find a used suit an shirt in your size from a reputable brand. Suits depreciate in value massively once worn, and in my opinion its better to have a nice suit than no suit at all rather than a cheap suit. Perhaps go to a suit shop to understand your sizes then go online?

Yes but only in the sale.

Idk if you can get something cool with that budget where you live. I hope so! But keep in mind that having a business suit comes at the price of cleaning and ironing and such! Maintenance of a suit is more expensive than that of simpler basic clothes.