OP I know you are a busy working mum, and I do know that not everyone on a PTA maybe understands that. Life is like that on many issues.
I have tried really hard to drum it into those at our school that it doesn't matter if you donate an item, or give your time for a stall or baking a cake, or come along and spend your money we are grateful for whatever you can do or give.
Because as long as you do something you are supporting the school and your children.
If everyone donated and no-one bought we'd have no money. And if you can't afford to donate an item then giving your time to run a stall can actually be more valuable. Volunteers can sometimes be the hardest to find for fetes etc.
Also while some parents would prefer to give a donations (and certainly I know at least two of the 4 secondary schools around here do this), there are plenty of parents who object to giving the school money for any reason.
Our local primary school asks for a donation towards the upkeep of its swimming pool & the qualified swimming teacher they employ in the summer. They also ask for fruit for KS2 children at 10p a day (KS1 get for free). A significant number of those asked don't pay. Some because they can't afford to and some because they don't want too.
The short fall is picked up by the PTA. I know many of those same parents (some who can't afford to pay, but also some who won't pay but can afford takeaways and more than one holiday a year) wouldn't volunteer to give money to school to save them having to donate to cake sales etc.
However some of those that won't pay for 'nothing' will come along and buy things at the school fete. And we always ensure that there is a range of activities at different prices to suit everyones budget.
I know one lady who can't afford to donate, she gives her time instead. And her children get to help on her stall and then get to have a free go on things after they have helped their mum a bit. So maybe if your children were willing to help sell the cakes they'd get given some for 'free'.
There's only about 100 children at our primary school. At Xmas we raised over £200 on the fete (santa's grotto is expensive and he also needed a new outfit and haircut this year!), but out easter fete raised over £400. Which I think is pretty good going.
Our summer fete is next week and I am not expecting huge profits, because this fete is about having fun while raising some money. It's about giving the Yr 6 a good send off, involving the community involvement and fun for all the family.
For example there were actually two older ladies waiting outside school today for the fete. They had the wrong week but were clearly keen to come along (OK I do admit that not much goes on in our village so any event is exciting!) And I doubt they'll be on the bouncy castle so are probably hoping for some tasty home made cakes.
PTA work jolly hard, and they get it from all sides. They're never going to please everyone. But they do understand that not everyone can donate or has time to bake or sell cakes. They appreciate just as much those who come along and buy them. At least I keep telling our PTA members that's the case. I certainly believe that.
And for the record, when I was working long hours I was never able to donate time. Now I work shorter (school) hours and I choose to give up time to plan, organise and run the fete. Give what you can, and if you prefer to give a monthly or annual donation (with gift aid) then go for it. Suggest it to the school, you probably aren't the only one who feels like that if the secondary schools around here are anything to go by. But equally there are people who like the fun, social side of cake stalls and fetes, and those who like to get something for their money.
Not every school event is about raising huge amounts of cash. Every little helps.