So I ordered a ds18b20 sensor last year from ebay. paid AUD $1.88 for it (including shipping).
Digikey looks to be $7 plus $20 shipping (and I'm not certain if those are USD or AUD)
As someone who doesn't do this for work - I've never seen/heard of digikey or farnel before. Maybe if I was ordering enough to hit the $60 free shipping limit - but I don't think I've spent that on electrical bits in the last year.
In Oz, you could try Element14 (which is Farnell rebranded). $50 for free shipping, or $15 under. The DS18B20's are about $7 on there too, so that's the correct AUD price.
RS is also a good place to buy decent mechanical bits and pieces (bearings, drill bits, etc) if you don't want to play the lottery on Amazon. They even do their own 3D printing filament which I've had some good results with.
If you need small quantities (like one-of), you should look at sample requests. This is still alive and well - almost all the big manufacturers still honour them. I've gotten some $40 RTD digitising chips from Analog, micro-coax cables from Samtec and lots of random bits over the years. You may need a non-generic email address, but that's easy to sort.
As someone who doesn't do this for work - I've never seen/heard of digikey or farnel before. Maybe if I was ordering enough to hit the $60 free shipping limit - but I don't think I've spent that on electrical bits in the last year.