I'm a programmer and work in a database language that has a very basic ability to interact with the internet. Stugs and Puntz have pretty well summed up what a programmer needs in order to create a custom program and also highlighted one of the main drawbacks.
I take advice from customers pretty frequently and the hardest part of the job is finding out what they really want. They will say they want a program that does this and when you've written it they will say "Did I say that, no that will never work, I really wanted it to do this." I imagine writing a program for a collective of punters with their own views on what they want the program to do would be a nightmare. (You could end up with as many software options as windows and be dead before you worked out how to make a bet the way you wanted.)
What I usually ask is how would you do this job manually and then try to automate a person's manual system.
Coming back to Shy's original post it looks quite an easy job. He enter's his horses and acceptable prices, the software logs in to IAS and downloads their prices and if they match up OK the software sends a bet to the selected bookie (assuming the bookie sight is enabled for automatic bet placement otherwise it would be rather more difficult although not impossible).
There are always problems of course. Shy enters his Kiwi horse's name as xxxx NZ and IAS happens to call it xxxx (NZ) so the two can't recognise each other. Then no doubt a week after the program was written one of the sights would update their software or change the format of their data or something and the program would need altering to accomodate that. I don't envy anyone who is trying to write a program which accesses the net (you wouldn't believe how crap the data on the net is) and has to please a group of people who all have different views on what it should do.
Anyway, although I'm not a specialist by any means on writing internet based programs I know enough to say "forget thinking of getting a program custom written". Too expensive. But I wouldn't mind betting there is a program out there somewhere which will do exactly what Shy or anybody else wants. There usually is and it's just a case of being lucky enough to look in the right place. Oh and of course being able to afford it when you find it. Because net based programming for diverse tastes is such a pain in the ******** I suppose it's bound to be expensive.