I considered a pump, but plumped for a small divers bottle for not a silly amount more. Iirc a 5L bottle (filled) was about £100, which should last me a year or two with my occasional use. A pump would certainly have been cheaper, but still...
Be aware though, bottles have to be pressure tested and certified every 5 years, and nobody will refill them without that certificate, so an ongoing cost there. Certifying/testing is about £35 I understand, if they don’t find a problem and needs to sell you a replacement bottle of course.
As with many things, they can't fill a bottle that is not safe, so the paid checks are somewhat of a cash spinner, as ADR2019 comes into play.
I am also led to believe it is 10 years for cylinder testing