There are low cost AVR programmers, such as [1]. Similar are available for much less on Aliexpress.

You can also easily use an Arduino, a solderless breadboard, a few jumpers and some software as an AVR programmer [2].

[1] https://www.sparkfun.com/products/9825

[2] https://www.instructables.com/How-to-Program-an-Attiny85-Fro...