check out equestrian direct surfaces
We just got our full weathered arena done (25 by 45m) not sure on the costing range because mum sorted that out but have a look at ELD 😊There very well known
Costs will vary greatly depending on area or accessibility.
For fencing we changed from wood to flexible rail horse fencing. It's much more durable, doesn't get chewed on, doesn't hurt as much if you fall into it, can't be chewed on. We've never had a horse break it after 5 years of turning them out in it.
You can also look into rope, and wood fencing.
You'll also probably need to buy more footing over time.
Some sands are very dusty. It's probably worth going for more expensive, less dusty sands because the products used to to remove lessen dust levels are very expensive, don't last forever, and only work with certain PHs in the soil.