There are two types of firebricks: hard and soft. From what I've heard hard firebricks take longer to get hot but are cheaper than soft firebricks. And soft firebricks the opposite. Is it imperative to use soft firebricks? I mean I'm making my first gas forge and I have a budget limit. Getting the amount of soft firebricks I need could cost upwards of 70$ usd. But hard firebrick from like homedepot could cost only 30$ usd. Which do I choose?

Did you not see Mickey's reply in your other thread? Look up K26 Fire Brick on eBay, they will be the best. Fire bricks are considered consumables and need to be replaced frequently due to thermal cycling of the forge.