I share your frustration. It’s far from the lovely experience many seem to have isn’t it!
I have had a differently frustrating experience to you. I didn’t have a problem getting quotes, but I measured the kitchen myself and went in armed with those. I figured they or the fitter could do a final measurement themselves when I’d chosen which one I was buying.
I wouldn’t touch Wren with a barge pole. Nice showrooms, nice staff...bad delivery record (damaged/missing items) and appalling after sales customer ‘support’. Just don’t go there.
DIY kitchens quality is better than Howdens, Benchmark or B&Q. Their show room is great (worth the trip).
IKEA - their cabinets don’t have a service void, (space behind the back panel, they sit flush to the wall so you have to run the pipes through the cupboards, a lot more work to install on service walls. Fine on non and more space inside). People seem to make lovely kitchen from IKEA stuff, but I’m not inspired in store.
Masterclass kitchens don’t seem too bad.
Then there are places like Second Nature & Quantum.
Have a look at places like Panelven.
IMO there are far better options than the sheds & Howdens/Benchmark for a similar price. However, out of that group I think Benchmark was the best. Magnet is about 50/60% of the showroom cost if your fitter has a trade account.
It’s very difficult to get good trades people around here, so fitting it is difficult to get quotes for. I’ve decided to delay an installation until the new year now, so have a little breathing soace. I just have to hope the kitchen doesn’t collapse before then 😂
Good luck!