How long's a piece of string...
Where are you? Up here (north of England), hay needs to be worked, so you'd be asking someone to cut, strow out, woofle, woofle again, probably woofle again, row up, bale. Further south you may only need to cut, strow out, row up and bale. Maybe woofle once.
Also depends on the thickness of the crop, how dry it is, what the weather is doing.
You'd have people available to stack the bales?
Estimate anywhere between 60 and 90 bales / acre. Probably about 4 hours work overall if the field is flat and easy to manoeuvre around. Plus time getting to and fro for at least 2, possibly 3 or 4 visits. And diesel for all.
Anything from £20 - £30/hour is reasonable for a contractor plus equipment, and expect to pay for travelling time too. Ours charges very slightly less but uses the farmer's diesel.
BH reckons it costs us £2/bale (using our own labour and equipment) to make small bale hay. Hereabouts it sells for £4 a bale in a good year.