I send money back to the UK every month, and have done for the last four years or so. Couple of things to note: I have sent sterling to LloydsTSB and to Smile (co-operative bank) - neither has directly charged me for receiving sterling. I have sent money from China Construction Bank and from HSBC and both of those banks have charged fees on each and every occasion.
Where a direct relationship exists between the sending bank and the receiving bank, then the figure that your (sending) bank quotes (accounting for the exchange rate at the time and adding their fee) is the final price you pay. Where no direct relationship exists, then the two banks must use an intermediary and usually this third bank will levy an additional fee of its own.
Of course, if your bank in the UK has to change HK$ into sterling, then you cannot guarantee what exchange rate will finally be used (as it will almost certainly have changed in the time it takes you to wire it), so it's always best to send sterling back. Essentially what happens is your bank in HK buys the amount of sterling that you request and then deducts the correct amount (according to the precise exchange rate of the moment) in HK$ from your account (plus their fee).
The bank in HK then sends this to your bank in the UK and in the case of HSBC you can choose whether it should be the sender or receiver who will take care of any additional charges that may crop up after the money has been sent (whether levied by your bank in the UK or by an intermediary bank).
To send hundreds of pounds per month by PayPal you would need a merchant's account, I think. This comes with monthly fees and may not be cost-effective.
I have found the various bank fees to be never too high and on the whole acceptable, especially given the stability, security and convenience of remitting money direct from one bank account to another by internet banking. Any alternative method would have to represent SIGNIFICANT cost savings for me to change the way I remit money. That might, however, speak more to my laziness than to my good financial sense.