Perhaps the organization where you're working can give you a helping hand to be able to participate in a work retreat. After all you are specifically concerned with personal development and not to celebrate a holiday.
Even though each employer is different, more and more organizations know a "personal educational budget" for their employees.
Many companies, (government) institutions and organizations spend, under conditions, a part of their labour costs on training. Increasingly there is, whether or not agreed in collective agreements, a personal/individual educational budget available. Usually intended for individual training, personal development and career support.
County officials in The Netherlands for example, know the arrangement that they, in consultation, may spend €1.500 over three years.
There are companies which, in the context of personal development and employer branding, make €1.000 or €2.000 available per employee for this.
Employment agencies appear, for example, to have 1% of individual labour costs for individual trainings available.
Reason enough to maybe consider making an inquiry about whether there are opportunities for you, within a present or not present personal training budget, to make a participation in a work retreat program even easier.