Both SMLS and Topping offer some small entry-level DACs around the $100 mark that will have an optical input and unbalanced (RCA) outputs.
You'll need a USB power brick for the SMLS as it uses that input for power as well.
Here's a Topping for $150 (the cheaper ones with optical inputs seem to be combo headphone amps):
Topping E30 II DAC Preamp Audio Decoder- 2xAK4493S Hi-Res XMOS XU208 DAC 32Bit/768kHz DSD512 DSD Direct Mode for USB/Coax/Opt Inputs RCA HiFi Stereo Digital Audio Decoder(Black): Amazon.com: Industrial & Scientific
www.amazon.com
This one comes with a remote and dedicated DC in with cable.