The shape affects the final cheese, which is why you see a variety of different moulds. (I think that is the convention here, moulds are used to form cheese, molds are organisms used to ripen cheese, although you will find both referred to as molds)
Shape is perhaps more important with mold ripened cheeses like Brie - a 4" thick Brie will not ripen the center before the outer edges are overripe. However, it does affect hard cheeses as well. Some hard cheeses are less affected by shape, but need to have the appropriate thickness.
You can make soft cheese moulds from yogurt buckets, but they will likely not take the stress of pressing a hard cheese. I started out with a basket and a 4.5" mould and follower (the hoop doubles as a Camembert mold, I have a couple more). That served me well until I started making larger batches, so I added a 7.5" tomme mold and a couple of larger baskets. So, you don't need to spend a fortune unless you want to make cheeses that require specific shapes, usually small white mold ripened cheeses.
Mold unit cost is small, but startup costs are high. Have you priced an injector or extruder lately? Even for simple shapes tooling costs can be tens of thousands of dollars. Can you imagine the government regulations and expense to certify your materials and process food safe? Then you only want one or two. I used to sell parts in the aerospace industry. A part that we sold to Boeing in lots of 500 went for $300, but when an airline called and needed one today it was $2,500. Part of that was what the market would bear, but a surprising large part was simply reflecting the small lot setup costs and cost of carrying the part in inventory. Yeah, it's frustrating, but I've found that if I factor in even a nominal amount for my time gathering materials an labor, it's not worth trying to make a mold myself. My girlfriend is trying to get me to apply the same logic to cheese making. Silly woman.