bicycle for 4 yr old grandson's birthday

Halfords did have some very good deals when we bought one for DGD1. We bought stabilisers separately (I sent for them) but wish we hadn't bothered as they were a real nuisance.
They were very good at giving advice on what was suitable.
Tesco sell them too and should deliver to your nearest store, if you have vouchers sometimes you can double them up for certain items.

I got a little one for DGD2 (with stabilisers) from the charity shop in vgc

Most cheaper bikes are quite heavy, but the aluminium framed ones which are lighter are very expensive.

Have you tried Gumtree or local Facebook sale pages? I got a lovely wooden play kitchen with pretend food etc for £15 from local sales site. There are often outgrown bicycles on there.

They grow out of them so quickly it sometimes seems like throwing money down the drain to buy a new one. Sometimes you can get good deals on children's and adult bikes from cycle hire centres. We have two near us and at the end of season, they thoroughly recondition some bikes and offer them for sale. They usually only have good makes. We nearly bought one for GS last year - saw it on their website but someone beat us to it so we ended up getting him one from Halfords. He's happy with it. I'm always seeing them at car boot sales as well, but the quality is variable and you never know where they've come from!

Granarchist, our DGS also did very well on his balance bike, zooming along with his feet off the ground. He also had a bike (from FaceBay) with stabilisers on it which he would ride around on. One day last summer, when he was 3 years and five months old we asked if he wanted the stabilisers taken off, we did so and that was it, he was off, no problem at all. I think balance bikes are great for giving them confidence. His current bike is a 12" and quite heavy. For his birthday in March there is a brand new bike waiting for him, 14" this time and at the moment we have left the stabilisers on for him to get used to it or he may want them removed straightaway. We got it from Halfords in the sale, £59 I think. It will be his first properly new bike.