access+vba+courses+london - Geographic locations and logistics

I have set up a database with records for each site visit (including address)and have a field for region to help operations staff group sites. However I am on my third revision of defining regions, and sites on borders between regions may not get placed in the best 'bundle' so started to think about another field to indicate next nearest region.

Is there an add on facility to effectively give the access database a lookup, or alternatively a purpose made logistics programme which will somehow take in data from our database, and preferably not too expensive (hundreds preferred to thousands)?