To suggest people give DS money rather than a present?

[Pepperpotts66]

DS1 is 5 in a few weeks and is having a big party. He is crazy about Thunderbirds and wants the new Tracy Island that comes out in August. I've already bought him the vintage thunderbird models off ebay for him and can't really buy the island too, plus it doesn't come out until after his birthday. I've explained its very expensive and that it could be a Christmas present or he can save up his pocket money and any birthday money he gets. The thing is he now wants to ask his friends and family for money on the party invites rather than presents and I'm not sure if people would be offended by this?

I was wondering if on the invite I put a small note saying that if people are stuck for an idea as to what to get him he is collecting money for Tracy island but that we don't expect people to give money if they don't want to and that we don't exoect people to buy a present if they don't want to. I'm so worried about sounding like we are presuming people will buy him things.

The thing is every year we end up with a pile of presents that he isn't bothered with so I actually think he's come up with a very sensible idea. He's very obsessional and only plays with a few select things, we are actually looking into an ASD diagnosis at the moment. Don't get me wrong he always acts grateful and says thank you for gifts but the end up in the bottom of the toy box unless they're a plane or a train.

Thank you in advance!

*put, not 'out'!

I obviously have an odd group of friends then as back in our party days this was standard practice. We used to specifically request no presents but if anyone wanted to donate a shiny coin (pirate parties helped here) birthday child was saving towards .... We'd then get lovely home made cards with inventive ways of presenting £1 or £2. Occasionally a home made present on the theme of the party or the saving up for toy.
On the occasions where there was no request like that often a group of us would get together and throw £5 into the kitty for a bigger present.
We home educate though so the class party thing where you don't really know the other parents don't happen the same. Plus all home educators experience the same nightmare battle against clutter so tend to be happy to cooperate with any attempt to lessen unwanted stuff.
Now mine are older, parties tend to be open invitations to picnics and soft play. Often to general community so will get newbies along, specific friends will get told it is for DS' s birthday so they will make an effort to be there. All birthday parent does is supply cake. Tend to get lots of hand made cards. The odd present off close friends.

I tend to ask the Mum what the child would like. Occasionally the Mum has said money or a voucher. I've always preferred to do the voucher. I wouldn't put anything in the invite, I do think that's really rude - some people will be able to afford much more than others and they shouldn't be put in that position. If someone asks I'd explain he's saving for said toy and suggest a voucher for Argos / Amazon etc.

OK to mention it if they ask for suggestions. Most people won't ask.

There are some replies on here that are unnecessarily harsh.
The OP is not asking for money, let alone insisting on it, she is just saying if people are stuck for an idea, cash would be welcome. I can't see anything wrong with that; not beng a planner ahead or bulk buyer of books it would save me a lot of trouble, but allows anyone who prefers to give a gift to do so.
She is concerned though that just by giving this sort of guidance, it looks as if she is making an assumption that presents will be brought. We all know that they will be, but are too polite to acknowledge it openly. Sorry OP, you are obviously kind and thoughtful but you need to be brave and include the sort of message you suggested, no other way round it.