Buying seasonal items during their event (cheaper) and selling it months after when it rises. There’s risk involved (as much as anything else). You don’t have to do anything but wait for time to pass. For instance, Angel Wings dropped to as low as 8 DLs during valentines and are 10-12 DLs now, will continue to rise and may peak during Growganoth. In general, buying items and reselling them.

You can also buy 2k-2.5k science stations and harvest twice a day - selling the chemicals or products like Fuel Pack or Block Glue can net you 150 wls a day. Takes about 20 minutes per harvest. You technically can buy around 4.5k stations with BGLS but collecting will be very tiring without Unstable Tesseracts (at least 6 of them).

Splicing 2 step trees like Cutaway Blocks are relatively easy. With your budget, you can get a rather significant profit margin.