Just had confirmation my orders being processed - they also add a 'small order' charge of a fiver, seven pounds fifty standard postage, and VAT - so 2 Kg is about £50 or so - but hey, if that'll make 100 litres of the stuff, as PleasePieMeMistress suggests, it's even better value than Natrasol...
That's actually more expensive than what I've experienced with Natrasol. My last order for 2kg of Natrasol was £ 32 + VAT and P&P which came to just under £ 42, but most importantly that 2kg of Natrasol made me 150 L of thick gunge.
There is also very little difference between Methylcellulose and Hydroxyethylcellulose (Natrasol). The major difference comes in their solubility.
Methylcellulose will try to immediately for a gel the second it comes into contact with cold water. A gluey layer forms around pockets of dry powder which is sometimes known as 'fish eyes'. However Methylcellulose won't dissolve in hot water, so the way Methylcellulose is mixed is by allowing it to disperse in hot water and allowing the gel to form as it cools down. Interestingly if you then reheat this gel it'll become solid but then melts as it cools.
Pure Natrasol will attempt to form a gel with watr immediately regardless of water temperature. However the Natrasol supplied by the Basic Chemical Company for gunge is a grade known as HR250. R grades of Natrasol have been treated with minor quantities of a chemical called Glyoxal during production. Glyoxal slows the rate at which the Natrasol forms a gel with water. The time delay caused by Glyoxal is shortened by hotter water. Natrasol mixed in 30oC water will require around 10 minutes stirring, Natrasol mixed in 10oC water will require 80 minutes stirring. It is not a good idea to quickly make buckets of Natrasol gunge by making tem in really hot water and letting them cool over night as Natrasol gunge gets thicker as it cools, what once was a thick hot goo will turn into a cold jelly brick.
TBH I prefer to stick to Natrasol out of cost and ease. When I want a really stretchy look slime I just add something called Polyethylene Oxide (Poly Ox). I found a link to a place that seemed to do some cheap Poly Ox in the UK, my last lot came from the US, I've not tied them yet. Its on my work PC, next time I'm there I make a note of it.