Too many variables to give a definitive answer here.
Most sites that do HPA will refill for free, most fill as per above to around 2500-2800 so your 3K is instantly running lower. The pressure your system needs will have an impact on shot count as well.
A lot of dive shops will fill your bottle for a couple of quid.
A site that runs HPA will (ideally) have at least one master holding cylinder fed by its compressor.
This allows them to run the compressor when required to fill and then just top up the cylinder.
They would fill players cylinders to less than the master cylinders pressure Otherwise without a master cylinder they would be running a compressor to directly fill each players cylinder, or running the compressor all day to keep the master topped up as each player draws on the air
The first player gets full capacity, the next a little less etc. (The bigger the master cylinder is and the lower and more often the fills taken, the further any given master fill will go)
Restrict fills to a lower level such as 2400 to 2800psi and everyone can get a matching fill. Top up regularly rather than filling from empty and the compressor has to run for less during the day
Paintball sites that cater for own gunner paintballers provide free air fills.
If the same sight runs airsoft then they will probably also provide free fills. This may depend as if there is only one HPA airsofter then it becomes expensive for them to kick in the compressor