Buses are good in Montenegro (at least along the Bay of Kotor, where they’re cheap and very frequent), but I found taxi drivers there tended to demand very high fares. There’s a single organization, apparently, which has a monopoly. In Cetijne things might be a bit different. At any rate I got a driver there whose prices were quite reasonable: Mr Vujovic Veselin, tel 069 310517. He speaks a bit of English. If you want to see the sights (Lovcen, Ostrog...) that's his speciality.
To get to Cetinje it's simple... there are regular buses either from Budva or from Podgorica. Getting to Mount Lovcen is simple, too - although there's no public transportation. Once you arrive at the bus station in Cetinje you'll find a couple of taxi drivers which are more than willing to drive you to the top and wait for you - for about 20 euros.
Our driver was amazing: although we didn't have any language in common, made every effort to communicate with us... we had a brilliant time and enjoyed his driving style, which I can only label as fast and furious. Eventually we learned that he normally races in the rally up Mount Lovcen, covering the distance in about 7 minutes.
It is possible to take a different road down from Lovcen, leading you directly into Kotor without going through Cetinje - it costs about 15 euros more and it is money well spent as you will have the chance to admire Kotor Bay from hugh up - and quite a beauty it is.
If you want to visit Lovcen Mausoleum, you should not pay more than 20 Euros going by taxi from Cetinje!!! The taxi driver will wait for you and bring you back. Natives told us that 20 Euros is appropiate. Taxis are available at the bus station.