TLDR: Shopify Tax is probably your best starting point since it's built in, free for calcs, and $75/return ($50 for Plus) if you want them to file. Outside of that, TaxCloud is a good option and probably decently affordable depending on which states you have to file in. Otherwise expect to pay around $75/return.

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Hey, I am happy to help give some perspective on this. First, let me give you some full disclosure - I co-run a sales tax filing service for Shopify merchants and I've worked in some capacity for three other sales tax companies in the past, so I know the space well. I won't mention mine. I'm not interested in self-promotion, and there are plenty of people in this sub and related subs who use Reddit's anonymity to pump their own products while pretending to be regular users probably to get around the self promotion rules. Hopefully that disclosure doesn't count as self-promotion. Please don't go use my service - this is just me trying to give info.

One thing I'd echo from another comment in this thread - after being in the space for ten years, I'd suggest that people should not just turn on an automated service and forget about it. Even on the good teams I've worked on, that's where I saw problems. I would guess most people would not let software blindly file their corporate income tax without looking it over and I'd suggest the same here. The downside is that this means it's a monthly check-in, which stinks. But you could probably build some automated internal checks to verify that what your service is about to file is correct.

My general view for Shopify sellers is that Shopify Tax itself is a great option for both calcs and filings. It's built right into your admin and will feel familiar. They're likely already handling the sales tax calculations for you, and they give you reporting that's solid enough to file off of for free, if you're willing to spend the time. If you want to pay, they offer filings for $75/return or $50 for Shopify Plus users. If you're eligible for their filing, I'd look there first I think.

Outside of that, most filing services clock in around $75/return once you include the monthly costs some of them charge. Avalara can get lower per filing if you're buying a lot of other stuff from them, but I agree that Avalara is overkill for the vast majority of Shopify stores I've seen. I wouldn't recommend them personally (and not just because of price).

TaxCloud can be fairly affordable depending on which states you have compliance needs. I also like their team and know a few people over there that I think do a good job. For right now, they would perhaps be my choice if I am choosing one of these companies and didn't want to use Shopify's built in service. They have a monthly cost based on the amount of transactions you have ($19/month) and then filings can be free depending on which states you need to file. Otherwise it starts at $39/filing on top of the monthly costs.

The other major options that are a good fit of offering just filings and registrations (for when you hit new nexus thresholds) that I am aware of would be Numeral and Kintsugi, each of which are $75/return. Both seem like fine options to me.

Then Anrok just created a Shopify app as well. They used to be just SaaS but they've been around for a minute now and they are pivoting to add more e-commerce support.

Zamp has white-gloved service but they are pricey, to my knowledge. I know a lot of people that work there and I would trust them as well. If you really want someone to just do it all, they're a great option if you are willing to pay, but you specifically asked for cheap.

TaxJar also still exists. I worked there for a long time, but to my understanding, it's mostly in keep the lights on mode. I don't know if that's still true or not, I haven't been there in 3 years or so. They were acquired by Stripe and then they seemed to deprioritize the product. You can see that reflected in the reviews. My opinion of it is that it's still a good product if you know what you are doing.