That's surprising to me. I've been doing 2-3 angel investments/year in Silicon Valley (while being a full-time VC), and I've never personally seen anyone ask for a $250k min check at seed stage. FWIW all of my investments are $10k (the max that my fund allows me to invest on the side), and I don't get pushback on that 90% of the time.
On a slightly different note, minimums are rarely set in stone. If someone says the min is $100k and you come back with "ah that's a bummer, I love your company and think I can help with X and Y, but I can only afford $25k," there's a good chance that suddenly the minimum will drop to $25k just for you. At least that has been my personal experience.