We just found this Simba Smoby Kids Basketball Hoop & Stand for a great price at Amazon, as they're selling it for just £14.99 with free Prime delivery. A similar set is selling for £50 at Argos so this looks like a super price.
This basketball set comes with a 16cm basketball, a base, an adjustable pole, a colourful backboard, a hoop, and a net. The adjustable stand means it can grow in height as your child does, as it's adjustable up to 160 high.
Some of the comments say that you can also detach the net and backboard and fix it to a wall making it last even longer as you could move it higher as your kids grow.
There's free and fast delivery with Prime, or free standard delivery when you spend £25 or more for non-Prime shoppers.