Suggestions for phone system refresh?

Our organization currently runs Cisco voice for everything (CM, CCX, ER, UC). Our phones are 79xx and are failing at exponential rates.

Current environment:
- 500 7961G-GE
- 10 7962
- 25 7936
- Most phones use Line 1 and possibly Lines 4-6 for organization speed dials
- 30 or so phones use Extension Mobility
- All phones are PoE (except 7936)
- Skype for Business Hybrid configuration (not currently integrated with CM, but there is future opportunity)

I am hoping the community can offer feedback or suggestions on the following:
1. Cloud PBX/PTSN? Our organization has been slowly transitioning to more Microsoft cloud services and I am wondering if we should position ourselves for Cloud voice services.
2. Cisco or Other? #1 might dictate whether we stay with Cisco or move to other vendors. Exchange might be able to replace Unity Connection (voicemail) and Skype for Business might be able to replace Contact Center Express (call queues, auto attendants).
3. New or Refurbished? I see a $1,000 new phone on CDW that is only $300 refurbished on third-party sites. If we stay with Cisco, should we purchase new or refurbished phones? We will not be adding the phones to SmartNet coverage, so is there a practical difference between new and refurbished?

Cost is the most important factor. SmartNet coverage is not cheap, by any means, and my general feeling towards Cisco is that they try to lock you in wherever possible. User acceptance could be a hurdle if we migrate to another system, but if the cost savings are significant enough I'm sure this could be tolerated.

I appreciate any and all feedback.