You won't find LED's for $1/bulb, but the total cost of ownership over X years is massively in favor of the LED.

Also I simply find it convenient that LED's just. don't. die. I haven't had to change a single bulb since I upgraded ~4 years ago.

I just saw some 2700K bulbs in Poundland (£1~=$1.38), at a selection of power levels. Not sure what the brightest was, might have been 60W equivalent?

I deliberately got a dimmer model because I wanted something to encourage my mum to sleep more; due to Alzheimer’s she has no idea what the time of day is any more, and has developed a fear of the dark and only sleeps with the light on.

You don't, not yet anyways. But if that 100w bulb is on 3-hours per day and you want a 1-year ROI, your replacement budget is probably in the $8-12 range.

I usually go to Ocean State Job Lot or Home Depot. There's a wide selection for $1-2/bulb. I like Cree or Philips as brands.