Reasonable Commercial rent increase? Chicago IL

[Lindsay M.]

I have been renting a commercial space to my tenants since I purchased my building 3 years ago at the same rate they were paying before. I have recently found that the space they are in is worth significantly more than they have been paying. On one hand they are great tenants, they pay on time and are relatively low key, easy to deal with. On the other, the lease they had prior to my purchase is much more like a residential lease than a commercial one, with me paying for a lot of maintenance and utilities that is not typical for commercial tenants. All together they are paying about $500 a month less than similar spaces and I do a lot of maintenance for them (I live in the building.) Their current rent is $1800 per month. They are a support group meeting place. I could really use this money but I don't want to lose them by springing a huge rent hike on them. What is a reasonable amount to raise the rent initially? Can I negotiate a rent raise by starting high and coming down to what they can work with? Do people do that? I really have no idea where to start I'm new to commercial rentals. I'm trying my best to be reasonable and still get a fair price for my space. I am located in Chicago, Thanks for any advice you may have.