You will only be able to use 2 vouchers plus a credit card for the reservation. Vouchers don’t cover taxes so in your case find a flight costing about $130 apply the 2 $50 vouchers pay the tax. When you then go to cancel the flight request the taxes be refunded to credit card (since that is refundable within 24 hours of booking)
next repeat one more time with voucher 3 and 4 once you cancel that you can use the 2 confirmation numbers to apply anytime you want later on and you technically got out of the taxes this way as well if you end up booking a $200 ticket later on of course if the price is higher than your 2 travel funds you would just pay the difference by credit card since you can only have 3 forms of payment on a reservation.
... View more