If it's just one bolt and you're in a bit of a pickle could you not just use a hacksaw?
Look on eBay and read reviews.
Angle grinder might be your best bet but try not to cut your body parts off.
Use goggles and proper gloves.
or pay a garage to do it
A rotary multitool can be slow progress, but can also be handy for certain jobs and is a decent tool to have at on your shelf. Ive got a cheap Vonhaus one (this one) and it works well. I can also highly recommend the Dremel EZ speedclic head and cutting discs. They allow a bit of give so the discs don't snap anywhere near as easily as the standard ones do