When I used to vape custard etc, I would buy jam on toast as a short fill from the shop as an alternative to DIY, didn't find it expensive (no, I don't earn loads either), back then I had a vape budget and it still came under it.
My DIY custards would have upto 8 flavours in it and I would always make a minimum of 1L.
I think cigarettes are about £10 a packet now, so technically £70pw, even a load of shop made juice comes in well under that.
Vaping is as cheap, or expensive, as we want it to be.
I buy 10ml of mixed fruit (£2),
add 350-490ml of pg/VG (£0 as it's bulk buy from a few years ago)
= shake it and it's ready to go,
I have a bottle of menthol of upto 18mg nic (99p) of which I add a few drops to my tank when I fill up.
= £2.99 cost for upto 500ml of juice
Many of us advocate keeping mixing simple, it keeps costs down.
The longer you vape, get to know what you like, what you don't, you will find ways to keep costs down, one of them may be DIY.