Negotiation on prices is frowned upon in public. If you want to talk to one of the many people that post here regularly (of which there are many) you might find one or two willing to do this for a reasonable fee.
The other “community support” way would be for you to contact the pros at Sangoma and buy support credits. As you need support, you put in a ticket and do your thing. This would actually by my first choice, since I don’t want to pay Sangoma to keep this software around, but there are plenty of people out there that should.
If they can’t support you, you can always fall back to “plan A” and contact one of the many people that talk about how they support their commercial customers. You’ll want to look at their advice (so do a little reading) and see what they say and how they say it. You’ll probably also want to find someone in your “relatively” local area. Hiring someone to do “ticket” maintenance on your system who is 8 time zones away can make for tense waiting time.