First of all:
1) If any of the changes were due to medical issues that prevented you (or an immediate family member) from flying, United will refund the change fees if you can provide a doctor's note to substantiate your claim. You can request the refund at
http://www.united.com/refunds -- choose the eTicket Refund option.
Change fee refunds
In the event that your travel plans change as a result of illness or jury duty, you will be required to pay the applicable change fee at the time of that change. Once this change fee is applied, you may submit a request to have the fee refunded.
2) If the one-way ticket is cheaper than the change fee, you should just buy a new one-way ticket.
Change fees are just part of the cost of buying a discounted ticket. There are tickets available that have no change fees.