So I did an approximation of the mint stamps. There are about 1500 of them with a face value of about $250. Now we all know that you can't sell these stamps for face value, but unless you are willing to purchase a lot of duplicates you can't buy these stamps at face value either. If one were to go to Subway Stamps or Golden Valley Stamps you would pay at least twice face value, with a minimum of probably $.20 per stamp, which would put the "value" of the collection at over $500, so in my opinion you got a good but not great deal.
You have now acquired the start to a nice US collection and I use the word "acquired" on purpose, because now the collecting starts and you will have to decide on what sort of collection you will have and each purchase will be a decision of price versus quality. I personally collect US 20th century (plus the Columbians), mint with centering Fine-VF. I stay away from the rarefied atmosphere of 19th century Americana and the XF and above, just too rich for my wallet.
Many of the US collectors on this site acquired a large percentage of these stamps at face value by going to the post office every week or so. When we would forget we would miss out on items like 1623c and have to get them later for a much higher price
At the end of the day the value of anything on eBay
is a dollar more than the third place bidder was willing to pay.