Pilotinmydreams - if travelling between Hahn and Frankfurt-am-Main, the only useful train station in between is Mainz, or in an emergency Koblenz / Ludwigshafen. For some bus routes (e.g. Mainz), you buy tickets from the driver, while for others you buy from a ticket counter in the airport terminal.
Bus frequency from Hahn airport to towns is not great - a 2 hour gap between buses is quite normal. Once the bus sets off, it's usually fairly speedy and goes on the most direct route with either zero stops or maybe 1 stop.
You can find bus times at
Official website of the airport Frankfurt-Hahn
You can also find train times at
bahn.com - your online travel booking tool for rail journeys, holidays, city trips and car rental
You can get a taxi from Hahn to Mainz (nearest proper station), but at 55 miles, it won't be particularly cheap - think about 100 pounds - and yes the taxi driver may be open to bartering on price for a good long fare. Then again, if you and your boss are going there for work, the value of your and his time might make it worth spending the money.
A taxi from Hahn to Mainz station will take about 1 hour 5 mins, while the bus takes about 1 hour 10 mins.
If arriving at Hahn, I'd probably say in priority order:
1 - if there's a bus direct to Frankfurt within an hour, take it - you'll save on time spent waiting for a train anywhere else.
2 - if there's a bus going to Mainz within 30 mins take it
3 - consider taking a taxi to Mainz and then train to Frankfurt
4 - if there's a bus to Ludwigshafen (bus continues to Heidelberg) within 30 mins, take it
5 - if there's a bus to Koblenz within 30 mins, take it
6 - spend the money and take a taxi to Mainz anyway
The route you should take really does depend on what time of day your flight lands at and departs from Hahn.
One final thing. Under no circumstances should you or your boss reveal to your counterparts in Frankfurt that you are flying to/from Hahn. They will likely regard you as unreliable cheapskate muppets and not suitable as business partners. Just let them assume you flew to the main Frankfurt airport like any normal business people instead.