A bespoke suit in Savile Row currently runs at around 5k, although tailorscum will do it for cash for less. There are lower priced bespoke suits but honestly you really do get what you pay for. Anyone who is any good works on Savile Row. You could spend 1500 quid on an utter bastard.
As far as multiple suits go, I would start at one good one if you aren't wearing it much and then perhaps get another in a year's time and build from there. Grey is perhaps more daytime and navy may work better for both but this is very much a generalisation as it depends on your skin tone, hair, personal style, etc, etc. Concentrate on fit, silhouette and quality, rather than fancy cloth and pocket details, coloured buttonholes and the like.
I can't remember where we got to with the rest of it but a decent pair of shoes and shirt will go a long way to making you look and feel good too.