FK-5001/9000 calculator replacement

Background
Some time ago, I developed a replacement for the stock, failure prone calculator module in the Focus FK-9000. This project was essentially a "two" off that I made for myself and Chyros. You can see the module on Chyros' youtube channel in his "Project F" at around the 10:30 mark. In the time since the video was posted several people contacted me expressing interest. I am finally looking at do a small run of these for those who are interested.

Details
The replacement will be a plug in replacement for the stock module and include a OLED monochrome graphic display. (Some minor modification of the the upper case is require for the display to fit). The module functionality will include:
* Identical functionality to stock calculator including memory
* Selectable RPN input mode
* Persistent clock with date
* Multiple configurable settings for clock format and style
* Eliminates need for stock battery
* Compatible with FK-5001 and FK-9000 that use the single KB/CAL key

Questions for those interested
1. Offline availability: The prototype included a rechargeable Li-on battery in order to support using the calculator when the keyboard is not plugged in and/or the pc is not turned on. For packaging simplicity and cost savings, I am thinking about removing the offline capability and using a simple coin cell to retain clock/date information.
Question: Do you consider offline availability essential even at higher cost/complexity?

2. Case modification The display used on the prototype requires that the plastic ridge that locates the stock display be removed. This modification is simple to perform and does not change external appearance. I have made some inquiries in hopes of finding a display that would not require any modifications and would have a higher resolution.
Question: Does having to modify the case turn you off from this solution? Would you be willing to pay more (~$20) for a display that does not require case modifications and has higher resolution?

3. Older FK-5001 and FK-8000 support: Older FK-5001 models used separate KB and CAL buttons to switch modes and the FK-8000 has a different mounting method and pin header. The module does not currently support these keyboards. If you have one of these keyboards and are interested, let me know. I will investigate adding support.

Pricing
I do not have final pricing yet. Pricing is on the conservative side to avoid surprises. Depending on final configuration, I estimate the cost to be:
Base module ~ $50-60
Offline availability ~ +$15
No mod display ~ +$20

If you are interested please respond or send me a PM with the answers to the questions. Also let me know what you think about pricing.