Hmmm...thats a tough one!
The only thing I would advise if you have a nice chunky budget like that is to consider buying from sellers in groups in order to share the cost of shipping across many ponies.
As for the rest of it; I was a long time finishing up my collection and if I am honest I found no way in particular that worked better. I had my list, I knew who I was looking for - and if I ever had to pick and choose between different options it would be either which seller I prefer or which pony I preferred - just favouritism
. Initially I would be looking for sellers who perhaps had auctions on for 3 or 4 ponies I was looking for and would focus on them above other auctions. But sometimes you actually find that sellers like that get more interest than the person selling just 1 pony or 2...so you can miss out on a bargain. But in general I found the most fun was just to surf around the Arena and Ebay and bid on or buy the ponies I liked the best
Nothing fancy or scientific about it.