Sails Marine Bait and Switch after purchase Monroe Connecticut

I purchased a marine air conditioning unit from the online site and was invoiced for the item and shipping. The shipping I agreed to and was invoiced for was $35. It is a reasonable shipping cost as the item weighs about 85lbs. Sails Marine contacts me the next day and asks for $160 for shipping. This is after I have received a copy of my invoice with the total including the $35 shipping fee. I had a quote done by UPS and they quoted $97.00 for shipping and this is with no discounts or having an account. I complained and suddenly the price is $140.00 for shipping as it has to go through their "Trucking company". I'm not sure why it has to go through a company that I've never heard of at a higher rate? There were multiple providers for that AC unit but the Manufacturer has raised the price and I can no longer get a unit at a competitive price. I have tried to be accommodating and have the item shipped to my office which will save them money but believe they should honor their agreement as I have honored mine. If they have made a mistake in their shipping quote then I should not have to pay for their mistakes. So they don't make as much on the deal as they had hoped. That is a learning opportunity for the company.