I suggest you purchase the life raft first. The reason for this is you will quickly, if not sooner, realize you really really need a dingy. I interpret your statement cruising the San Juans to really mean the Gulf Islands and Desolation Sound and Jarvis Inlet as well. If this is the case, for example in Desolation Sound, you'll be on the hook most of the time and won't be able to get off the boat at all unless you have a dinghy.
So by purchasing the life raft first, you very quickly purchase the dinghy second. I'm on Vancouver Island and most larger craft here don't have a life raft but do have a dinghy.