Hi, At the first stage you need to focus on industry as you mentioned in the question. Do some research to collect analytics of the business, how many companies is doing companies which this industry.

Secondly, if you have tight budget, then you should identify the (MVP) version, minimum possible features which complete the business flow of your application. Also, you can find a company that could support you in development if your idea is powerful.

Another possibility is you can contact some good consultant to give you technology suggestions.

I would like to tell you a complete process for your product development

Design Phase In this phase we first developed wireframes, It is a pictorial depiction that provides key elements of the UI (fields, buttons, icons, layout, etc.)

Then we decided the style guide, It is standardization of UI elements, UI frames and end-to-end experience.

In development phase, development front end and backend for the application will be done

Then there is a quality assurance (QA ) phase in which we done unit testing, integration testing and performance testing.

Then there is a deployment phase and your website will go live.

I can help you with low budget development as well as product promotion with great business development plan

The best way is to go to tech community and offer them to buy from you.

1) Search digital marketing and SEO agencies from Linkedin and google reach out to them , put your financial analytics or revenue of your business in front of them and ask them to buy your SEO company.
Usually , a medium or large size company might be interested

2 Take your proposal in which you should mention the best things about your company, how it will be beneficial for some one who buy it. Trust me, Take written material with you and meet the tech and marketing related companies near you.

3 Email your offer to all the SEO related startups and persons who you know them can help you in this regard.

4 You can also advertise it in newspaper and classified sites which are popular in your location.

Firstly , The most important thing what are you selling. Identify the key features of your product its main strengths.Secondly identify the correct prospects to whom you should sale it Otherwise all efforts will be useless. Just think who is possible buyer keeping in mind few things
1 Your product or service is fit for a person. Example if you want sale a beauty cream you must go to girls of age 16-40 who can buy it or a Car value of 100000 $ to a businessman having good turnover yearly
2 The forum or the way to reach out to your targeted audience.
Door to Door, Online through digital marketing, Through TV Radio etc.
3 Whenever you pitch some one . Make strong entrance which can create an interest
like

Do you want to be look more beautiful than your friends?
Do you want to become million dollar business ?

Conclude and suggest that the product best fit for a customer.
4 Identify how your product give value to a buyer and why he should buy

All the above mentioned points will help you , Trust me , I have been doing million Dollar IT sales every year Using these techniques

Yes, Before going to set a campaign one must check the google Adwords keyword competition tool to find the best keyword which are searched by the audience. You need the site owners to come on your website? you can use little general keyword like "Rewards for site owner GSGO"

i can give you the best advise how to use social media to reach the targeted audience and how to fetch email addresses and phone numbers of site owners and inform them through cold calls and email marketing