Look at these too:

KJN (https://www.aluminium-profile.co.uk/) (will ship long lengths)

Motedis (inexpensive, but limited on lengths)

Mitsumi (shipped from Germany, but has some fancier cutting services and profiles)

The length limit is probably not a problem if you're building non-industrial machines...

Also aliexpress for cheaper profile fixings, t-nuts etc.

Alan