View historic USD prices when transactions were made
I was also looking for similar solution and have come up with a manual one.

Note: you need to know the Bitcoin address of the sender and receiver, or transaction hash. let us suppose we know a bitcoin wallet address 


  3BtSyeNf24tEXkEYKiMmDjM98W7Yqudh3w


and it belongs to person A, following steps can be executed to know about the transaction details

Step 1: Goto www.blockchain.info and enter the respective address into website's search bar.

Step 2: resulting page will show transaction details which are as follows

      a. Transactions performed = 2
      b. Total Received = 0.02608688 BTC
      c. Final balance = 0 BTC


[explanation: Respective Address had two Transactions, 1st. it received 0.02608688 and it spent complete amount because its remaining balance is 0 BTC. Each transactions is explained below.]

Step 3: Evaluating transactions

      a. **First Transaction** hash is 
         0d704a15bd8d56812dff9d067c0510afb4185190d2816513dd8eca777b7ec72c
      b. This transaction was confirmed at 2017-10-09 16:08:56
      c. Using historic Bitcoin price reference at coindesk.com/price/,it
         was found that at that moment 1 BTC was equal to 4722 USD.
      d. Hence, first transaction shows that person A received 123 USD 
         worth of bitcoin. (0.02609 BTC * 4722 USD = 123 USD)

      e. **Second Transaction** hash is 
         fe5bd13f81d26166937efc472f8a30090e7f30e721517ad212bc06e48f8e1e96
      f. This transaction was confirmed at 2017-10-15 16:05:17
      g. Using historic Bitcoin price reference at coindesk.com/price/,it
         was found that at that moment 1 BTC was equal to 5700 USD.
      h. Hence, Second transaction shows that person A transfered 
         accumulated BTC for 148 USD . 
         (0.02609 BTC * 5700 USD = 148 USD).     


Step 3: Net difference 

      a. Person A gained 20% in 6 days (one perspective)
      b. Net worth of holding is zero because wallet holds 0 BTC


I hope i cleared some of the confusion.