Take a bus from either Podgorica to Budva or vice versa. You will have to ask the driver to drop you off at the road. Tell the ticket collecting guy well ahead of time using basic communications, hands & feat, etc. and he'll be more than willing to drop you off on the main highway. From there start walking and hitch hike. It shouldn't take you too long to get picked up.
There are direct buses to Rijeka Crnojevica from the Podgorica main bus station but they may be hard to find and not run very often.
