Relationships

Boyfriend invited me on a family cruise but I'm not sure I can afford it?

My boyfriend invited me to go on a cruise with his family in December and I am expected to pay my way. They are still shopping for deals but it is likely that the trip will cost me $1000-$2000 total (flight, room, food, drinks, and spending money).
My finances have changed significantly over the last month as I am starting grad school. My work hours are reduced and I've made large school related purchases so my savings are reduced.
I have $1500 but I'm hesitent to reduce my savings further considering I won't be able to rebuild my savings for some time.
I'm hoping to get an internship position by the end of the summer to boost my income. If I get an internship, affording the trip won't be an issue.
I would love to go as I've only traveled a few places, but I'm hesitant given my finances.
And lastly, my boyfriend is also in grad school and his mom is paying for him and all of his siblings who are recent law school graduates to go. I get that I'm not "family" so there's no reason for her to pay for me... but I am wondering if it would be rude to ask either my boyfriend or my boyfriend's mom if either of them would be willing to cover some portion the trip for me ($500 or less)? Is that out of line?
As a grad student my boyfriend also doesn't make much, but his parents cover all of his expenses other than food.
Boyfriend invited me on a family cruise but I'm not sure I can afford it?
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