The grinder is the most important bit of kit, more important than the coffee machine itself. A bottomless portafilter is a useful diagnostic tool which helps you to see if you are getting the tamp right, but it cannot compensate for a poor quality grinder.
If you cannot afford a decent grinder just yet, then use pre-ground and don’t spend money on anything else until you have saved up and bought the grinder.
The only thing more important than the grinder, is the beans. As with all foodstuffs, there is no substitute for good quality ingedients. Be prepared to pay for good quality beans.