Yes, you can get a travel medical Insurance for a visitor coming to the US for a short trip. The policies cover only new medical conditions and travel emergencies. Any pre-existing conditions, preventative care, routine checkups, etc. are not covered. Some policies may cover for acute onset of pre-existing conditions.
Learn more here: Travel Insurance: Pre-Existing Medical Conditions
You can get quotes and compare policies here:
Insurance rates are regulated by law. You can't find the same insurance plan for a lower price anywhere else