A family member has done this a couple of times now.
One was for a wedding present and the other a christening one.
Basically - she's sent me a text thanking me both times for our gift (I think the wedding gift was worth about £20 and the christening one about £10). Which ok, fair enough, it's nice to have a card but any kind of thank you is nice.
But I've found out that she's sat down and written cards to those people who spent more on the gifts - so both times my Mum and Dad have been given cards for their more expensive gifts. My brother was given a card for their wedding gift (expensive) but a text for the teddy they gave as a christening gift.
Is this perfectly alright? I just feel a bit... I don't know...poor relation I guess. But I'm happy to be told AIBU, really, it's not a major issue!