Amazon Echo dot for £24.99 if you own a sonos product @ Amazon (£24.99 Prime Accounts / £19.99 Student Prime)

Using the recent deal of £5 free when you top up £25 (account specific)
£5 when you buy £25 top up

And the other offer of £6 when you buy a £30 voucher. (account specific)
£6 when you buy a £30 gift voucher

I used these offers too, worked out £8.99 for my DOT effectively.