From the east coast you have enough Avios to fly Business (60,000) one way and economy the other way (20,000) with 17,000 left to spare. You could go anywhere in Europe in Zone 1 (4,500 each way) or Zone 2 (7,500 each way) with those remaining 17,000 Avios. Examples in Zone 1 would be Paris or Amsterdam, examples in Zone 2 would be Madrid or Venice. Even though you have to fly through LHR, so long as the layover is less than 24 hours on the way back you will avoid the UK Air passenger Duty which is a significant part of the carrier imposed fees so that would cut cost.

Another way to save cash is to book two one ways. The carrier fees when you fly out of the US are significantly higher than flying out of the UK. So when you book two one ways you get hit with the higher US to UK fees on the outbound leg, but have significantly lower fees on the inbound UK to US leg. To book two one ways you book the outward bound leg online as normal using the companion pass as a one way trip. You can book the return online as a one way as well, the catch is that you need enough Avios to initially book it without the companion pass. You then call up the call center and have them apply the companion pass to the return leg. When they do that they will refund half the Avios used for the return leg. In your case, as an example if you choose a Zone 1 destination you could book the outward bound in economy using 20,000 + 4,500 Avios and the companions pass, leaving you with 72,500. That would leave you enough to book the return for 2 x (20,000 + 4,500), or a total of 49,000 miles, leaving you with 23,500 Avios. When you call in to apply the companion voucher they would refund you 24,500 increasing your total back up to 48,000 miles, which you can then use elsewhere. After that you may even be able to upgrade the original bookings to Premium Economy with those 48,000 Avios if space is available.

If you have any Ultimate Rewards points you could transfer them to Avois (it is almost instant) to increase your balance so that you could go business one or both ways using two one ways.

Its convoluted to reduce cash costs. It can be done but you will have to work at it.