Hi Dan, of course you can, just ask. From my experience of Richer Sounds, they are more than helpful and could probably put together a good system at that price. However It may be instructive to note that MP3 is a compressed format and will not normally sound as good as straight CD, I personally recon that a £25 CD/DVD player from Tesco would sound better, and would hardly alter the budget.
Whilst I realise that no 'self respecting' Hi-Fi buyer would ever venture into Tesco for musical Nirvana, the reality is that the 'bottom end' just got better, so much better that it now challenges the 'top end'. Check out a bottom end class 'D' amp, it may only be £90 but don't dismiss it, then keep all the real dosh for a serious speaker system, you will be amazed at the results.
John...
PS please don't be intimidated that £100 on leads will do anything as it won't, virtually all dealers are keen to sell leads as their 'mark-up' is so much greater than the equipment.