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Digital Optical output and digital coaxial output only offers lossy bitstream sound quality. For the best sound quality you would want to use a HDMI connection to a A/V receiver to experience lossless sound quality that is bit for bit exactly the same as the studio master.

I am guessing that you want optical audio output to support a legacy A/V receiver that does not have HDMI input.

You will have a hard time finding a Blu-ray player under $50 with optical output. The reason is, manufactories are trying to keep prices low and even on some high end models they have eliminated the optical audio output. Most under $50 Blu-ray players just have HDMI output which offers lossless audio.

I normal only recommend OPPO, Sony, and Panasonic Blu-ray players since they offer reliable firmware updates and offer a better level of quality compared to some other brands. If you’re A/V receiver supports digital coaxial then you could go with a low cost Sony Blu-ray player for under $60. Even the top of the line 2014 Sony Blu-ray players for over $150 does not offer optical output anymore. According to the spec sheet the new Panasonic Blu-ray players like the DMP-BD91 does not even have any coaxial or optical output.

Recommendation

If you’re A/V receiver does not support HDMI lossless audio, then I would recommend purchasing a Sony Blu-ray player like the BDP-S1200 for $59.99 or less (requires wired internet connection for BD-LIVE and streaming. Other Sony models have WI-FI).

If your A/V receiver or sound bar does not have a digital coaxial input then you will need to purchase a coaxial RCA to optical audio converter for around $12.00.Therefore any Blu-ray player on the market that has a digital coaxial audio output can be converted to optical audio output with a low cost adapter for around $12.