i find that gasless is crap, i get a much much neater weld with gas, also find it much easyer with gas also i find gasless wire is expensive.
would rather use pub gas than gasless
I pay £7 a reel 
if your doing any quantity of welding £7 for .5kg is expensive wire ( for mild steel anyway ) gasless wire dosent go very far ether.
BOC are rip off thingys they tryed charge me over £120 to fill a 20 ltr + 100 PA rental so i told them to feck off never been near a BOC agent since, i would try and get an account with a local supplyer they are about.
as said i use industrial gases a lot of the bottels are air products so would recomned looking for an air products distubutor.
10ltr bottels are £4pm fill for £20 - 25
20ltr bottels are £5 or 6pm ( i think ) fill for less than 40 quid
50ltr bottels are £7pm fill for less than 60 quid
if you get stuck for gas i know of someone with a BOC account that chould have the bottel filled for you or give your bottel a top up