The right choice depends less on budget than on complexity and on how much the two of you agree.
DIY
Cheapest, since you pay only the £628 court fee. You carry the risk of errors and there is nobody to check the financial side.
Guided online service
A fixed price, plain-English questions and a prepared application. CalmSplit is £159 per person, one-off. It suits uncontested cases where you want structure without hourly billing.
Solicitor
Best where there is conflict, significant pensions, a business, international elements, or safety concerns. Billed by time, so costs vary widely.
This article is general information about the law of England and Wales, not legal advice. For advice on your situation, speak to a solicitor.