Your banker likely does not know how to value a sub nor would know the value of the head end and outside plant. Best bet is to hire a consultant to do a complete inventory to show fire sale prices and cost to replicate. This way your banker will know what they are getting as collateral should you default. I recently did a system valuation for two way 860 Ghz system with similar sub count (600 internet customers with the potential for 2000 subs).
Make certain the system has a fiber backhaul agreement already in place as that will be a significant cost.