Firebase is good, but not cheap.

If you want some alternative SupaBase may be a good consideration.

It also provides a self-hosted option for the advanced user.

check it on this link: https://supabase.com/

Commercejs is another headless e-commerce API and it is also the one I feel fits most cases.

It provides a free plan with 2% transaction fees, sounds like SnipCart but it also provides paid plan for 0 transaction fees.

If you don't know which one to choose then maybe commercejs is it.

check more information form their website
https://commercejs.com/

swell provide all the APIs we need to build a headless e-commerce website and the community plan is free to start.

Basically, you can use it to host all of your products and orders.

check more at this link

https://www.swell.is/

There are a number of choices for the headless cart solution, SnipCart is another one.

The reason I list it here is that SnipCart is one of the oldest in the game.

They are charging a 2% transaction fee + payment gateway fees, without a monthly fee making it fit for most less traffic e-commerce sites.

check more information on their website.

https://snipcart.com

If you have worked with FireBase FireStore, it should be easier to start with Fauna.
The free plan offers 100K Read, 50K write and 500K compute with 5GB storage should be enough for most personal projects.

https://fauna.com/

I like this this most.

https://http.cat/{http-status-code}

idb.js is a tiny (~1.06kB brotli'd) library that mostly mirrors the IndexedDB API, but with small improvements that make a big difference to usability.

import { openDB } from 'idb/with-async-ittr.js';

async function demo() {
  const db = await openDB('Articles', 1, {
    upgrade(db) {
      // Create a store of objects
      const store = db.createObjectStore('articles', {
        // The 'id' property of the object will be the key.
        keyPath: 'id',
        // If it isn't explicitly set, create a value by auto incrementing.
        autoIncrement: true,
      });
      // Create an index on the 'date' property of the objects.
      store.createIndex('date', 'date');
    },
  });

  // Add an article:
  await db.add('articles', {
    title: 'Article 1',
    date: new Date('2019-01-01'),
    body: '…',
  });

  // Add multiple articles in one transaction:
  {
    const tx = db.transaction('articles', 'readwrite');
    await Promise.all([
      tx.store.add({
        title: 'Article 2',
        date: new Date('2019-01-01'),
        body: '…',
      }),
      tx.store.add({
        title: 'Article 3',
        date: new Date('2019-01-02'),
        body: '…',
      }),
      tx.done,
    ]);
  }

  // Get all the articles in date order:
  console.log(await db.getAllFromIndex('articles', 'date'));

  // Add 'And, happy new year!' to all articles on 2019-01-01:
  {
    const tx = db.transaction('articles', 'readwrite');
    const index = tx.store.index('date');

    for await (const cursor of index.iterate(new Date('2019-01-01'))) {
      const article = { ...cursor.value };
      article.body += ' And, happy new year!';
      cursor.update(article);
    }

    await tx.done;
  }
}

https://github.com/jakearchibald/idb