I don't know the Myrtle Beach area that well so I'm not highly capable of speaking on the property value. However, if you are renting out a vacation home of 3 bedrooms then you will probably want to get much more than $150 a night for it.
Also, a hard money loan can be a very tricky endeavor. Unless you already done so I would suggest finding out every piece of information you can from your lender about the entire loan structure. Most seem to only lend for a few years at most, and if you can't pay off the loan at that point it is possible they will simply take over the property itself. I've never seen it done but I have heard of people who have actually lost their property to a hard money lender, not for being late, but for not paying off the loan completely after just a couple years...and the homes were still producing just fine.
I don't want to scare you away. Hard money can be a great way to get the ball rolling. But if you can't refi or pay off that loan completely then it may also be a great way to loss the property. BTW if you have already found some hard money lenders would you mind letting us know who they are?