A group buy is a deceptively big undertaking, especially when ordering outside the EU, so make sure what you are getting into.
If you wish to do a group buy on the forum, I will issue some guidelines. The most important being it is strictly non-profit.
If you haven't done much buying from overseas, here is a rough outline of what is involved.
Any transaction will be at the mercy of your bank's (or paypal's) exchange rate. They will also charge a non Sterling transaction fee (around 3%)
Anything over £15 (that's goods plus shipping/insurance), gets hit by VAT, and a handling charge by Royal Mail (or whoever is the onward carrier) of £8 - £15
Over £135 you get VAT (20%), then import duty (variable, depending on goods category, but usually around 10%) and finally the handling charge.
https://www.gov.uk/goods-sent-from-abroad/tax-and-dutyAs a rule of thumb, if you spend $100 you usually end up paying £100 (more if the exchange rate is bad).