Personal interest vs benefits - coughsyrup, in your case, it would hinge on whether your choice of a legal career is absolute or tentative.
If tentative, it may be well worth the finances for the sake of personal interest where this opens up engineering and other science careers as usual.
If absolute on law, it's probably not as worth the engineering degree at the end of the day, because even if you specialise in science-related legal areas like intellectual property law, construction and the like, the extent of application of such knowledge is still confined (although substantially beneficial).