I think everything is relative to what you are paying, the prices for places like the Sila Evason for 1 night equals an average salary for 3 months !!!! So it depends what you are paying and what are the alternatives. There are countless places on Samui to choose from so I would think before booking a package.
There is a simple calculation to find out if it's a good deal.
Find out from any air ticket broker ( even at weekend many are open ) what they will charge for a flights. then look at transfers, then calculate what it is costing per night. Do remember that 'pacckage deals' are per person, whereas hotel room charging for a double/twin are for 2 of you, note this with care as it it something many people do not notice or think about. Idf someone asked me in Bangkok for a nice private place on Samui I would probably suggest the Sandalwood Villas, they run at between in English pounds about 70 to 100, that works out for 7 nights at between 255 to 350 English pounds per person.
If you can tell us more of how private you want, whether you would prefer private villa to a resort or wehatever we can give ideas. Although place like the Sila offer great luxury and no probelm to enjoy of you can afford don't make the mistake of thinking you have to pay huge amounts for nice accommodation, I would personaly never pay more than USD 50 ( I guess about 22 english pounds ) a night anytwere in Thailand and for that I can get 3 to 4 star quality no problem at all.