3) Using an Arduino Nano.
Number 3 seems like I'm wasting a lot of resources too (feels like "throwing an Arduino away").
Is there any other alternative?
Sounds like you need the ATmega processor, crystal, and USB-to-Serial hardware, which comes to about 90% of an Arduino (Nano or UNO).
If your sketch can run on an 8 MHz Arduino you could use the internal RC oscillator. That would save the cost of the crystal and caps (about $3). I have seen articles about using cheap ($3) cellphone data cable for USB interface so that might work with an ATmega328P to give you most of an Arduino UNO for about $10.
The ATtiny85 only has 8 pins. You have to keep Vcc and Ground. You probably also want to keep Reset so you can re-program the chip without a High-Voltage Rescue Shield. I think they left out the serial port, too. Might make that USB-to_Serial cable useless.