The cheapest paid social media advertising platform depends on various factors like your target audience, budget, and campaign goals. However, based on average costs per click (CPC) and cost per thousand impressions (CPM), here are some of the most affordable options:  

1. Twitter:

Low CPC: Twitter generally has the lowest CPC among major social media platforms.
Targeted Audiences: You can target users based on interests, demographics, and behaviors.  
Quick Results: Ads can be seen quickly, making it ideal for timely promotions.  

2. Facebook:

Large Reach: Facebook has a massive user base, allowing you to reach a wide audience.  
Detailed Targeting: You can create highly targeted ad campaigns based on interests, demographics, and behaviors.  
Diverse Ad Formats: Facebook offers various ad formats, including image ads, video ads, and carousel ads.  

3. LinkedIn:

Professional Audience: LinkedIn is ideal for targeting professionals and B2B businesses.  
Cost-Effective: LinkedIn ads can be relatively cost-effective compared to other platforms.
Lead Generation: It's a great platform for generating leads and building brand awareness.  

Read more : The pros and cons of LinkedIn

4. Pinterest:

Visual Focus: Pinterest is a visual platform, making it ideal for businesses that rely on images and videos.  
Engaged Audience: Users on Pinterest are often actively seeking inspiration and ideas.  
Lower Competition: Compared to other platforms, there's less competition for ad space.

Tips for Keeping Costs Low:

Set Clear Goals: Define your objectives to allocate your budget effectively.  
Target Your Audience: Focus on the most relevant audience to maximize your ROI.  
Test and Optimize: Continuously test different ad variations to find what works best.  
Monitor Performance: Track your campaign's performance and make adjustments as needed.
Use Free Tools: Utilize free tools like Google Analytics to analyze your website traffic and user behavior.  

Remember, the cheapest platform isn't always the best. Choose the platform that aligns with your target audience and campaign goals. By carefully planning and executing your social media advertising strategy, you can achieve maximum results with minimal cost.