Syndnems hire center in Dorchester stock hobbyweld,
Blandford motorfactors do sgs I think.
Those are both rent free,
I think if you use less than 2-3 bottles a year rent free works out cheaper than a boc contract but do a serch on here as there are loads of threads about price comparison
If there is a boc agent near you it might be worth checking prices (or find one of the threads on it)
They do a hobby deal which is cheaper han the normal rental and they are doing 300bar bottles now as well I think.
Personally I just go for whatever is most convenient for me to get hold off. I dont mind paying 8.63% more if the place is open at 7am on a Saturday.