Okay so I am low on that grey gummy sealing tape for vacuum bagging, is there anything else that's just as good. Can wide sellotape be used to seal the ends of a vacuum bag if the mould was going directly inside of it? 

Yes it should work - and no its not as good as the gummy sealant tape.  Many vacuum bags have been made with a variety of tapes - and many work.  Be prepared for challenges, but when it comes down to it vacuum bagging isn't an all or nothing thing and you may have fine results for wet layup.  Duct tape works ok too. 

Edit to clarify:  For wet-layup - sure, in a pinch.  For infusion or prepreg - don't risk it!

For debulking with tube-bag I've often just folded the bag over a bunch of times and used one of those folder binding strips or two pieces of wood and spring clamp to close it off with no tape or sealant at all.  If air doesn't get in - you win.  Good luck!

I would say no. It might be, that someone has successfully created a leak free bag once or twice, but it is definitely not a reliable method. Tacky tape isn't that expensive. A single failed attempt will cost you that much more that it is 100% worth it's money.

Exactly ^ 

You really have to think about what it will cost if it doesn't work, rather than what you will save if it does work.