your better off saving up for the best you can afford, rather than just going for whats available "now"
cos you will regret it in the long run..
save up for an amp, then a sub.... rather than a package, cos you will end up spending twice... upgrading if you get a package.
i learned the hard way.
also, try some of the pioneer stuff.... its awesome quality now. (never used to be)
and the new Vibe gear is braking ground with its digital amps too.... bargains are to be had at your local halfords too.... like a full Fusion Power plant sub and amp package for £149.... 450W kit (RMS)
^you have a good point but there are some packages out there which do offer the option to upgrade esp. if they come with a 2/3/4 channel amp... and some of those packages do work out cheaper sometimes... For example:
Where buying seperately the sub would cost £70 boxed and the amp £90... and wiring... £30... a total of... £190... so its a £50 saving... so there are exceptions but I mostly agree with you that buying seperately can be best if you think you are going to upgrade... and I have had a similar experience...
...and in terms of upgrading... when you think a 2/3/4 amp will be enough for a 4 speaker set up... think again... depending on the speakers of course... I have found that it was cheaper and better to buy another Blaupunkt Velocity Reference VA4100 (£150)... than to go for an Audison 6 channel amp priced at £650... my situation was that the DLS 7x10s were power hungry and so were the Rainbow Comps up front... 4x100w RMS was not enough from one amp so now with a second amp it is 2x300w RMS front and 2x300w RMS rear...