Mobile Development barrier to entry

It's likely that you can install unsigned SIS files too. Check App Manager settings that the Software Installation setting is "All" and not "Signed only".

To get signed SIS files, there's Open Signed Online which allows you to get your SIS files signed for free, though with IMEI and some irrelevant platform security capability restrictions. If you stick with the test UID range and do not plan to have a wide audience, you can point your users there.

The PyS60 runtime installation files are already signed and are best delivered separately in any case.

The use of J2ME will also require you to pay for application signing fees if your application is using 'protected' APIs (for example using networking). Another drawback of J2ME is that the consumer handsets support different sets of certificates depending on the operator's security policies.See this article for more details.

I recommend sticking with PyS60 for your needs. It is a great development tool, but you will need to swallow the certification costs for distribution.