To think you don’t ask for a present of this value…

Grandma might have said oh anything will do and DH chose it. Why are you annoyed at Grandma. Have you even had a conversation with DH about it yet?

I've never heard of a smaller bottle of perfume being cheaper proportionally than a larger bottle.
110ml = £30
200ml = £70

Is this what you're saying OP?
Which aftershave is it?

You sound a tad controlling OP researching behind DH back - you could just have a conversation with him.
Also how is this GP's fault?

So your husband is the issue, not them.
Is there a reason he thinks you can afford £70 when you think otherwise?

Do you share a bank account completely or does he have his own money separately?

Do you share an Amazon account, did it come unboxed or did you just decide to open his mail?

Is there a chance it was on offer?

Why did you even think you needed to look it up?

Either there's a massive backstory about him not being trustworthy with money or you are being controlling.

And that’s fine, the point remains he clearly feels differently to you; so you need to speak to him. Not us and agree, as clearly you both have very different views on what is an acceptable spend.

I have a £30-40 limit for close relatives, a £60-80 limit for my daughter.
If I want to buy anything over this I get others together to buy as a group. Since starting to do this family have approached me about shared gifts when in other circumstances they probably would have spent more than they have planned because there's a particular gift they wanted to buy.

Oh, and a 5% mortgage rate is low.... a traditional average would be 7% or 8%. (I will ignore the fact that some of us remember paying 15%!).
If you haven't factored in a likely increase, then I think there are bigger issues to consider, tbh.

Context is everything though. Did DH ask for ideas and get a range of responses like he drinks this red wine, wears that aftershave, is in to model trains etc. and he just picked that one without really thinking because it was on amazon and therefore easy? Does Grandma actually know how much the aftershave costs herself as I have some older relatives that are still stuck in their head at 1999 prices? Or if they are very well off are they just out of touch and oblivious to the fact it’s a lot for you, especially if you don’t see them that often?

I wouldn’t be annoyed at Grandma just based on what you’ve posted but I would have expected DH to have more sense. I would expected him to return it, shouldn’t be an issue if it’s from amazon, and he should instead get him something more appropriate like a half decent bottle of champagne should be under £40 and that seems far more appropriate for Grandma’s boyfriend that you see twice a year.

Every bit of this is odd to me.

Nothing wrong with granny making a suggestion - DH didn't have to go along with it.

Weird that he thinks you can afford this but you don't. Why do you see your finances so differently?

Odd that you didn't just say, Are you mad, we can't afford this and then discuss.

It's much meaner to send a copy of the thing someone wants than a small amount of the thing someone wants.

But you’ve said you’re not close, and see them twice a year. How are they likely to know whether or not you’re struggling or working every hour under the son? If they’re wealthy, your grandmother just probably threw a few ideas out there without considering your finances, about which she probably doesn’t think much…? And again, you complain they’ve never helped you out financially, but would you really expect handouts of money from a distant family member you see twice a year?

This.

YABU for checking on your husband's spending - I would never do that. It's up to him what he buys/spends.
But it's also odd for any adult too actually ask for a birthday present - isn't the normal response "oh, don't bother.... just buy me a drink sometime"? So the grandparents are a bit odd too.

I agree that you should send the big bottle back and get a small one. Try All Beauty, they're often cheaper for fragrances.

I don't understand why you're cross with the grandparents when this is clearly a husband problem? He didn't have to buy it and if he chose to do so he didn't have to get the larger bottle. Why are you annoyed with the grandparents they've literally done nothing wrong?

Then that's your solution. How hard is it to have the conversation with him without getting cross?

"Jesus, Dave, that's a lot to spend on grandma's partner. Why not get the thirty quid bottle?"

Honestly, so many problems on Mumsnet are very easily solved just by talking to each other.

Can you swap it?

Send it back and order the 110 ml. I would.

If you only see them a couple of times a year they probably don’t know as much about your finances as you think. You also don’t know what gift they asked for. Did they specify what size bottle? Did they give DH a range of gift ideas and he chose? Did he want to spend that much?

I think you’ve flown off the handle here.

Google a dupe for the aftershave. Send the original one back and swap it. Think nothing more of it.

Life is too short

I’m also annoyed at his grandma for having little concept of cost

She was asked for a suggestion. She suggested. It was 100% then down to your husband to say that was too expensive & tell her how much you planned on spending. I wouldn't have a clue how much aftershave cost either