You could snag one of those M1 MacBook Airs on sale ($750) at Amazon (mentioned on MacRumors earlier today):
Apple’s thinnest and lightest notebook gets supercharged with the Apple M1 chip. Tackle your projects with the blazing-fast 8-core CPU. Take graphics-intensive apps and games to the next level with an up to 8-core GPU. And accelerate machine learning tasks with the 16-core Neural Engine. All with...
www.amazon.com
This is a baseline model, but it's still a solid machine at a bargain price...and it should last for a long time. The 8GB of RAM is a bit low for a modern laptop, but by comparison the 16GB model on Amazon is about $450 more expensive (about 60% more expensive more than the current price of the baseline M1 Air).
To add onto this, I recently switched from the machine
@tubuliferous linked to a 15'' M2 MacBook Air 16 GB / 512 GB. I'm not a teacher but I do corporate training and teach on average 2 2 hour training sessions a week (sometimes more, sometimes less depending on material we have to cover with our teams and how many new hires we are taking in). My day to day work: stuff related to my training sessions like powerpoints, material preparation, system onboarding - and lots of paperwork, metrics charts/reports, and web app usage. I found the 8 GB of RAM was totally adequate for this.
I did upgrade to the 16 GB and while my system metrics on my Mac are much happier (ie lower overall memory usage), I don't actually notice a true performance difference (ie the 8 GB machine could do all I needed and still felt fast).
I think you probably really have two routes to go here:
1. Since budget is a concern, try to save as much as possible. The $750 price tag on the M1 Air a heck of a deal and that unit will last you for quite some time. I don't anticipate office work or casual web browsing to need much more than this over the next 6-7 years
2. Spend extra now to allay longevity concerns. My recommendation here would be a 16 GB Air. Apple sometimes has really good prices in their
certified refurbished listings although glancing through it today, it looks like they only have units with more high end options listed.
You can buy external storage to supplement the available space on my computer. So if you have (or take) lots of photos and things, you don't necessarily have to pay a lot up front for more storage on your computer when you can easily buy something down the road to store all of that information. If you have a lot of apps you want to install, it might be worth it to spend extra. The types of data you'd need for work won't take up a lot of space relative to the amount of storage available in even a baseline unit though it might not hurt to take al look at how much storage you are using in your current computer to get an idea of what you might like.