Sometimes dealers sell chems just as cheap as online.
Which chems are you looking at? There may be differences.
Alklinity up is baking soda from the grocery store - it also works on you PH if your alkalinity is low as well.
rhtubs has some good prices on chlorine - Doc sells 5 lbs for $30 and it is the best deal I have seen online. Chlorine (dichlor) can have fillers and stuff that don't do anything. Doc's chlorine (all clear) is 97% available chlorine compared to some dichlor that may be 52% - the higher the available chlorine the less you need (sometimes confused with active ingredient). Make a $60 order and S&H is free - Buy some Sea Klear clarifier and MPS along with the chlorine and you are at $60 (I think)
Since I don't use a lot of chems I can't comment on the other 1,000 chems available.