In a scenario where a company is transitioning from a traditional Public Switched Telephone Network (PSTN) to a Voice over Internet Protocol (VoIP) system, they need to evaluate the impact on their existing telecommunication infrastructure. If the company currently has 100 analog lines, and each line costs $50 per month to maintain, what would be the total monthly cost of maintaining these lines? Additionally, if the company plans to replace these lines with a VoIP solution that costs $20 per user per month, what would be the total monthly cost after the transition? Calculate the difference in monthly costs before and after the transition.