The biggest problem for Bitcoin mining is not the start investment, but the cost of your electricity.
You are fighting with all the world and in some places electricity costs are very low.
If you can have a so very low cost electricity provider, then you can start with only one ASIC miner, even an used one ($1000, for example).
I think that is no longer true, even if you have free electricity, then you are paying retail prices for your mining equipment (and for many individuals also shipping and VAT) while big farms are buying equipment in bulk (by the container) and as business they can deduct a lot of costs. They get the more efficient hardware far cheaper and earlier than 'small' users, so you can't compete with them.
You used to in past... but not anymore