Hi Peter,
I suggest you to opt for SAP Business One.
With SAP Business One you can work with Production,Purchase,Sales,CRM,Finance and as you mention you can have Inventory module also.
Its an complete Business Application and with fine tune customization as per Business requirement you can easily customize the software according to your requirement.
Through Query builder, you can create management reports for not only Inventory but Sales and Purchase analysis along with Production reports also and of-course finance would be an complete package.
Inventory module gives you complete tracking of your In and Out of stock with their valuation.Several reports you can analyse like Inventory Audit report, Inventory Posting report, Stock report, etc..
and with ADD-On you will have extra advantage specially.
Above all it is very mush cost effective as compared to R3 and other products.
You can always have an DEMO from SAP Channel Partners can have clear all doubts with them before purchasing.
Thanks,
Harshal