Take a look at adafruit and sparkfun
replyYou can find kits that have a selection of sensors - enough to get started and experiment
Aliexpress is king for cheap IoT modules/accessories
replyI'd go with a more reputable vendor unless you're on a really tight budget because Aliexpress isn't even that cheap, all things considered. There are fake chips and really low quality parts out there that will waste your time.
replyYou can get a range of ESP32 boards from Digikey for $5-$8 and you'd have to scrape the bottom of the barrel to get them much cheaper than that on Aliexpress.
If you have a nearby hackerspace or similar, check it out.
replyLikely they will be able to help you choose and guide you.
For me the hurdle was less about finding equipment and more being able to learn from experienced people.