The easiest and cheapest solution is to use the CUCM integrated conference based solution. This will require you to purchase or add additional PVDM on your voice gateways. You can either do this/branch or use a group of dedicated branch gateways for this.
You can refer to DSP calculator for PVDM details.
I suspect in CUCM we can have maximum upto 8 sessions,only 8 conference party can participate..so shoud i need to go for webex session?
That is inaccurate, with software based conferencing provided by CUCM you can have up to 128 G711 participants, with DSP based conferencing you can have up to 64 participants if I recall (when using G711) and 32 when using G729, or 32 and 16, I forget :-) Number of sessions would depends on amount of DSPs you have for which you can use the provided link to DSP calculator.
Same as AD-hoc conferencing, limited by bridge capacity, you just need to remember to adjust max meet me participants service parameter which defaults to 6 in CUCM.
Meetingplace express has been dead for several years (version 2.1 was last and we are on 10.5 across the board), in fact MeetingPlace as a product is dead as well replaced by CWMS.
In addition to Deji's response (+5), you need to provide more details, i.e. do you require scheduling ability, recording, how many participants in each conference and total number of conferencing sessions, this will let us know if you would be OK with CUCM based conferencing or require external bridge such as WebEx.