Hi,
So I know it's not what you asked for, but alongside seeking out a penetration testing company, it might be worth looking into carrying out some basic checks internally for free - just as a starting point, the Cyber Essentials certification is worth looking at - actually getting the certification costs money, but the assessment questions are free, there's a free Readiness Tool, and you can even book in a free 30 minute consultation if you're a small or medium enterprise (this is probably actually the least useful out of the three, though, because 30 minutes is likely to primarily be a sales pitch):
There's a reasonable chance that you might be able to identify some low-hanging fruit that you can fix without having to spend on consultancy hours, and save more of your budget for this project on the more complex still that actually does require specialist knowledge.
This is predicated on the assumption that you have IT, a tech-savvy member of staff who can check this stuff, or a managed service provider that can assist, of course.
(source - I'm a software engineer for a financial services company who also has a cybersecurity certification)
Thanks,
Harry