You COULD go after him legally if you had a work CONTRACT signed and notarized, which is something everyone should put in place.
Taking money meant for travel expenses to commence employment is called THEFT BY CONVERSION and is prosecutable. Try taking money from an employer of any sort meant for a relocation package without relocating and see just how far you get before you're arrested. $300 however isn't worth the time/expense.
Never send money...unless of course you're willing to spend money to recover it.
