Two winters ago while I was in Marsh Harbor I had to get an upgrade chip for my Garmin 192. This was necessary to make the GPS properly read the chart chip. (I know it was my fault for not checking before I left the US)
Anyway I called Garmin and had them ship one to me. They shipped US Priority Mail, it arrived in Nassau the next day and spent six weeks in limbo before being forwarded to Marsh Harbor. Added to the cost of a chip was $50 Customs and a Brokerage Fee. The basic cost for the chip was a $50 deposit. Fortunately I do carry paper and always have them available. I was also able to instal Plan2Nav on my smart phone.

As Chris said - If you ain't got it, live without it, or find someone coming from the US to bring it in with them.