Probably can’t go wrong with the Boss VE-22, or look if NU-X has a knockoff

What kind of music do they mainly like to sing? It would help in figuring out what their needs are, some pedals have more special effects which would be good if your friend was into more experimental music, or have different delay chips used for the loops which can be more hi-fi or lo-fi depending on the chip and the clock rate they use and all that, some let you adjust those parameters. For general use I think it's really hard to beat the Boss RC-505 or RC-202, they are well tested and have a good community around them as well.

The TC Electronic Ditto X4 is a lot smaller, it's not quite as flexible as those but it's cheaper and easier to use I think. If your friend is a little more experimental you can check out the Alter Audio Time Tosser which is dsp based and allows you to mangle your loop/samples a bit more. The Chase Bliss Mood is also worth a look if they are into lofi/warbly kinda stuff. You could also look into something like a TC Helicon VoiceLive Play which is a pedal effect specifically for vocalists and includes a looper, I have no experience with this one tho

If you're not familiar you can go to reverb.com which is a marketplace for musical gear especially, but a lot of vendors sell stuff there new as well, you can find deals on b-stock and some good sales sometimes. If you want good support I would buy at sweetwater probably

If you're meaning a physical control unit, Ableton pads are pretty reasonable I think, with some maybe US$60 or so? I guess a key point is whether it's meant to operate standalone, or in conjunction with software running on a computer. I think most want to run the software.

How your friend's mic connects would also be a factor, plus knowing what their existing equipment is. Some mics need power, some don't (like the classic Shure SM58), and you might need a digital interface, depending. I have a "Focusrite" (model Scarlet 2i2) for such, and it's nice because the two inputs are multipurpose, taking both 3-prong microphones as well as guitar patch cables.

Also of note is that there's free software (both DL and online) for looping and effects, so it comes back to whether their computer will be involved or not. I think smartphones can work, too.