It's hard to imagine an organization who can afford to run
a network using BGP to announce a class C block and not
be able to afford $1250 per year.
The Internet != for-profit-only corporate netspace.
In that case, the organization is not an ISP which
means that they are not growing which means that they
don't need as much of ARIN's services, therefore they
can swap their class C block for an ARIN /24 and only
pay $100 as an end user. Presumably ARIN could be convinced
to waive the one-time initial allocation fee in this case
since the initial allocation happened years ago.
Then, having joined the club that 99% of us belong to,
they won't have any problems with using newer services
like BGP cert signing.