I have worked on a B2B marketplace for technology and advised for a few B2B vertical marketplaces as well. This was for different clients in US, Asia and Middle East.
You will need:
1. ability to attract integrators and sellers
2. Easy onboarding
3. Low listing fees
4. Great marketing team
5. A compelling reason to adopt your marketplace instead of alternative options and "current ways of doing business".

If you have these, your traffic will start growing, which would lead to signups and so on.

You can re-build a few webpages and contact forms for free, except for website hosting costs. The design will cost extra, if your previous website design was custom made, and has special features.
Use a software like wordpress, and see if you can spend time to learn it. Else use a wordpress developer, and they can give quotes for the rebuild. They can cost $20-$100 per hour.
The website design requires thought, and if re-design is involved, it can cost a few hundred to a few thousand dollars.
And do not spend money on some custom theme or plugins for Wordpress, start with the free ones, they are normally sufficient for such a project.

Give me a call if you need guidance on this.
I have launched many sites, and advised clients in Europe and US on this type of projects.
Basic SEO for wordpress is not expensive either, you can start for free and see how that works out.

It depends on the ticket size of the sale. I recently sold a brand new SaaS product for ~$2500 with a cold call. But there were about 20 calls that went unanswered before we converted. For emails, we had a far higher conversion rate, but conversion was defined as getting the client to click and accept a meeting invite. Note: This is just a single example, and is not representative.

It's true, GDPR and other regulations limit the channels you can use for marketing.
Ultimately, SaaS sales should start with genuine leads. You can get leads by optimizing SEO/SEM. You can buy leads from other sources.
Next step is to research these leads. Then based on geography, seniority, number of potential contacts in the firm, you identify your approach. Spray and Pray is probably not the best approach.

For many clients freemium works.

You can setup a call with me for follow up questions.

I assume that you are selling office space across Asia?
I have tried a similar approach for getting technology clients in new markets. There are a few ways by which you can qualify your leads.
1. You should setup google alerts for activity on "remote teams Asia" or some similar keywords.
2. Scan LinkedIn or job boards for hiring activity in your target cities.
3. Look at the government websites that publish information on new ventures being setup. You can scan them to see if they have large parent firms overseas, or the amount of investment they are committing.
4. Co-working spaces are also used as temporary offices, before new offices are leased or investments from VCs are finalized. You should track firms renting space there.

You can call me if you want to discuss lead qualification in more detail.