Sure, I can give you some suggestions for a PC build suitable for office use and running Microsoft Office and Excel.
Here is an example build that should fit your budget:
CPU: AMD Athlon 3000G - ₱3,700
Motherboard: ASRock A320M-HDV R4.0 - ₱3,300
RAM: Kingston HyperX Fury 4GB DDR4 2666MHz - ₱1,500
Storage: Kingston A400 120GB SSD - ₱1,500
Power Supply: FSP Hyper 400W 80+ - ₱1,800
Case: Tecware Nexus M - ₱1,100
Total cost: ₱13,900
This build should be able to handle basic office tasks without any issues. The AMD Athlon 3000G comes with integrated graphics, which should be sufficient for Microsoft Office and Excel. The 4GB of RAM is enough for basic multitasking, but I would recommend upgrading to 8GB if you plan on running more demanding applications in the future. The Kingston A400 120GB SSD should provide enough storage for your needs, but you may want to add a larger hard drive in the future if you need more space.
Overall, this PC build should be a good starting point for your office needs within your budget.