Alternatives to buying props
Pre-covid you'd be able to go to a yoga class and either the studio would hold the props there, or the teacher would bring them along to every class. Now, even if you're allowed at the venue, props are not allowed to be shared around, and whilst in lockdown some people do not have access to props and may not want to invest in them either. Here are some alternatives:
The thick yoga mats that are used nowadays didn't exist when yoga asana were first practised, and have only been used for fewer than 50 years. If you don't have a yoga mat, you can just use a towel or rug. Some people prefer to do this anyway and cotton mats are available to buy. However, it is definitely better to have something cushioning your joints, so you could create a thicker surface with a few towels, blankets or rugs. You can also adjust these under knees and/or wrists when necessary.
A strap is so useful and luckily easily replaceable with a hard or soft belt, a tie or a scarf. Any long (approx 1-2m) piece of material that isn't easily breakable will do.
Blocks and bricks are used for different purposes but are mostly quite easy to replace.
To sit on: use a folded blanket or cushion. This is more comfortable than a block anyway!
To place under limbs during certain poses: again folded blankets are useful, especially as you can fold them into different thicknesses to fill the space you need to.
To lean on during certain poses: you could use a box, a very big book or a pile of books- just make sure they're securely piled and not wobbly or at risk of falling over.
A bolster is a luxury anyway, amazing to put under your knees whilst lying in relaxation, or to sit on for meditation.
To raise you knees and flatten your lower back during relaxation, again you could use rolled up blankets, cushions, or even a spare rolled up yoga mat if you're lucky enough to have more than one!
Sitting for meditation, you can sit on a cushion or folded blankets.