Price to Hire a Full time team of about 10 coders for 6 months at a minimum. I do a fair amount with A&D, and this is not the type of thing that a person or partners do. It takes a corporation. Here is a run down of the steps
Analyst and you sit down for many meetings (Depending on how pickey you are this could be months)
Analyst compiles requirements and sends to Developer
Developer spends months figuring out how to meet the requirements set forth by the Analyst.
Developer Sends Detailed Project outline to Analyst and Analyst reviews it with you. This loop continues (and the debt piles up) until there is a clear step by step plan.
Developer sends code to the programmers who start working on this. There might be a senior developer that breaks things down so an OO approach can be taken (better but costly and then you have to have OO programmers, they do not come cheap)
Coders then code to the design.
Once there is a working program it goes to QA where it is tested to ensure it meets the specs provided. If there are any errors it could go all the way back up to the Analyst, then trickle back down to the coders.
QA then sends the completed project after you have paid for it.
Be prepared to drop six figures plus for this.
Considering OO programmers make over $40 an hour and thats the lowest paid position in this.
Next unless you have a script that can compare website prices (once again $^3), you have to convince other sites to pay you to "advertise" for them. Getting a clientbase of customers is hard and until you have a client base no company will pay you.
Also there might be Copyright issues if you take their prices for their item with sku of ... and link to their site.