I habe a 100x50 foot barn. Built in the 40s on our 14 acres. Im lucky the first 1.4 section of the barn has a workshop with 4 inch slab and 220/120v 55 and 25amps. Like 8 outlets.. water/sink filtered from the house. And a chimney for a wood stove lol.
But the 1.2 section of the barn is dirt like yours.. dusty as hell.. the other 1.4 is 6 horse stalls. For the middle of the barn i actually used horse rubber mats. Theyre heavy as hell.. like 1 inch thick.. and about 6 of them fills up a space for my other Jeep so i csn work under it without the dirt.
Id like concrere in there.. but pavement is probably cheaper. Although if you do the concrete yourself and just have a truck dump it. It might be cheaper to do actually. All youd need for that entire section is a yard maybe two. And gravel for the base