I started with a jupiter 500, which is a cheaper option than a yamaha 275, then moved onto a yas-25 (which is a great sax). Depending on your budget, i would either go for a jupiter 500 or a yamaha 25 (good quality second hand is the best for both... you can get some great deals then sell them at the same price, or in my case, more!) I bought my jupiter for £250 brand new, played it for two years (actually put a dent in the bottom of it) then sold it second hand for £270! The same story for my yas-25, bought £600, played 6 years, sold £650!
But what really makes a difference is the mouthpiece. I would recommend starting with a selmer C* (probably second hand) which second hand should cost you about fifty quid.
Also, one youve been playing for a while, try out different brands and strengths of reeds. I have two mouthpieces (one plastic, one metal) and use a different reed strength and brand on both.
PS. don't be tempted by gear 4 music. I had to borrow a brand new one of their saxes when mine was in being serviced. Bleargh...