Wedding drama

So my boyfriend and I are getting married in 8 months. It's going to be a small wedding with only 50 people (we sent out 25 invites as everyone gets a plus one). We're getting married in a small church out of town and only inviting family and the wedding party (which includes three friends each for myself and fiancé). The reception is being held at a really beautiful hotel over a lake- We can't afford to have a larger wedding due to the cost. We actually wanted a smaller wedding but since my fiancé and I both have large families the numbers are larger and we're not even inviting our whole families just immediate family and close relatives. 
Anyways some of my friends are being really nasty about not being included in the wedding. They're not close friends either- I'm only inviting my best, closest and oldest three friends. I'm having a bridal shower that my mum is throwing for me- she's inviting the family that wouldn't physically be able to make the wedding due to health/money reasons and some other family/friends that don't know me but want to celebrate with my mum (they're totally ok with not going to the wedding since it's out of town and have never met me by the way). My wedding party is invited but none of my other friends are because I don't think it'd be polite to invite them to the shower and not the wedding/reception.
I'm not having an additional reception afterwards to celebrate with everyone and I don't want to. It'd be too expensive and I'll be too busy after the honeymoon. My wedding and small reception is already costing us enough money. So that's not an option. My mum suggested inviting them to the shower and telling them that they should not bring a gift. They can come to the wedding, but not the reception because I can't afford that. But that all seems so rude! But they're already really angry with me. Most people are really understanding and nice about it (some have actually asked to come to the ceremony/shower even though they're not invited). I don't know what to do! Help please!