For bare root, you'll need to wait till late autumn/winter. Bare root are cheaper, but can't be planted during summer. Google bare root rose suppliers UK on the web. That said, I wouldn't call roses low maintenance... they always want deadheading, pruning annually, spraying regularly during spring and summer for black spot, mildew and blackfly, together with feeding and worse, they're thorny. Mixed shrubs are classic low maintenance plants, a mix of evergreen and deciduous ones which flower at different times or have interesting foliage, maybe with two or three perennials mixed in.

Goodness I agree - 50 floribundas would be hard work!

I've only got four roses and I'm thinking of ditching 3 of them because their needs are too high for me. Much rather have a scented shrub like a Daphne or a beautiful Pieris.

How about clematis, lovely flowers, various sizes, can be grown in pots or not and lots you can cut down to the ground.
https://www.thorncroftclematis.co.uk/advice/care-guide.html
Spirea come in a variety of sizes so you could mix the colours of the leaves or flowers to give a display.

Roses certainly are labour intensive and rather spiteful! But I can understand your desire for roses and wouldn't like to be without them myself. 50 floribundas sound a bit daunting unless you are fit and able but if you are set on them and want cheaper ones why not try a Sunday market? We have one near here where there's always a wonderful plant stall which sells good quality plants including roses, (bare root in late autumn) at very reasonable prices. At least you can see what you're buying and it makes an interesting morning!