if you make a shiduch, it is a great mitzva and a zchus, and would be noble not to expcet $, unless you gave up a job and repalced it with shiduchim.
If you met your bashert thru a shadchan, OTOH, money is most appropriate, even a very small amount, according to what you can afford. Let them choose what they want to use the moeny for.
$750 is very nice. if you can afford $250 or even $36, all acceptable. Remember to include a card showing your appreciation. That will be cherished and long lasting…
So, may I wish you a Mazal Tov?
Yes, there is a category MO Machmir, and there are terrific group of people under that category. Attend a a minyan 3 times a day, kovea itim, and usually college educated. The more machmir- the better. You wont see their engagement pics in a way that would upset his Rav or her HS teacher…, or myself.