Hi Laura and welcome! Im a newbie here and its a really nice place to talk coffee :D
I have just gone through the exact experience as you so can point you to a few threads where the collective knowledge in them from the community here can help you make a decision :)
Basically Im was in the same position as you - (very) cheap machine, looking to upgrade it, but then aware of the need to buy a decent grinder (it seems you already realise the importance of the grinder so youve got a head start already ;))
This thread talks about how much of a budget should be spend on the grinder vs. the machine - if on a small budget, should I ignore upgrading the machine for now and spend the entire budget on the grinder? Turns out "yes" was the answer :)
This thread talks about my grinder options, and whether I should go as high as the Mazzer Mini. How much are Mazzer Minis in Canada compared to the Rancilio Rocky and other options? YMMV
Finally, after much searching throughout the country (New Zealand), I was able to find a well used Mazzer Super Jolly for a fraction of the cost of a new Mazzer Mini. This thread details the decision process and advice of others on how to clean this machine if you do get a 2nd hand one that has never been cleaned (like mine).
At the end of the day this is a summary of my advice:
How important are cosmetics? A brand new Mazzer Mini will probably fit under your kitchen shelving and look great. But if you can fit a larger Mazzer Super Jolly (many people here use it without the hopper attached or have been able to source a "mini" hopper that fits in a fraction of the height), and dont care too much if it has chips and/or cracks to the paintwork, then you get a slightly faster grinder that is "truly commercial" in some senses and is likely to last you a long time. The machines are easy to get serviced, and replacement burrs are inexpensive.
A second hand Mazzer Mini may be an option too - I cant really advise about those but Im sure they would be fine also.
There are other options - not just Mazzers. I opted for a Mazzer due to NZ being a small place and not having wide penetration of other brands - because they are common I presume they would be easier to service if required, and resale values higher if required. If you have a shortlist Im sure people here could advise you further :)