_"How do I approach my manager to see if split payment is possible?"_

I was in a **similar situation** for a quite expensive training course regarding OTP's - we ended up in **splitting the costs** since **budget was already carved in stone**. I don't think it's unprofessional as @Fattie stated in his answer since, in regards to mentioned circumstances, it was **still a win-win situation** for me and the company. 

I would simply **contact your manager in writing** stating the importance and the **possible benefits of the training** for the company and the team as well as mention that **you are aware** of the fact that the yearly consolidated budget would be exceeded by X-amount of $ if all of your team-members will attend. 

In the next paragraph I would ask him if **they would accept** that the difference would be **payed by the individuals** attending the mentioned training and if they are keen that all members of the team would attend and the dates of the training **wont interfere with any important schedules** (Keep in mind that they might need some or all members in case of an emergency, important meeting, deadline, milestone that week).

Something along the lines of:

>Hey [enter name here]! Our team recently found out that there's a really useful training event named [enter name here] held at [enter location and date-range]. Our company and the team would really benefit from this training-event because [enter plausable reasons here].
>I am aware that the yearly budget for our team is exceeded by [enter $-delta here] since the sign-up fee is around [enterx-amount of $ here] for each person attending. Would it be possible that the difference is payed by each individual that would like to attend?
>Also, would the date [enter date-range here] interfere with any important, upcoming schedules, meetings or milestones/deadlines?
>Best, [enter your name here] 

**Note:** Make sure all of your **team members are on-board with the idea** and are also **willing to attend and pay-up** for the difference. Also keep the option in mind that if someone doesn't want to attend, they might be **willing to pass their share** of the yearly training budget **to the other members** to reduce the difference for them.

Another option would be (as mentioned by the others) to ask your manager to talk to their superiors, notifiying them that a temporary budget increase this year in order to meet the amount needed would be beneficial to the company for certain reaons.