What small cheap ship can fit combat probes launcher and still put up a good fight?
as usual, we will answer to you that it is situational.
Every ship can fit combat probe launcher
But “put up a good fight” means that you select a target which you can fight. And a real good fight means that there is some equilibrium…
Probably nothing execpt a T3D because a expanded launcher takes a lot of fitting.
The T1 exploration frigates have enough cpu to fit an expanded probe launcher, although you may need to fit an engineering rig or module to fit tank and dps. I 'd choose the Heron since it has five mid-slots, making it extremely flexible. It’s a respectable pvp ship. I don’t have much experience with the other T1 explo frigates.
Otherwise I’d choose any of the T3 destroyers. They are very economical for what you get.
Alternatively bring a depot and fit/unfit the probe launcher as needed. You can combat scan your target then attack it in a combat fit. You can’t have your cake and eat it too, your combat effectiveness will be rubbish.
T3 destroyers are specifically bonussed to be able to fit an expanded probe launcher, and they put up a pretty good fight.
However, it might be worth noting that many fights and ganks can be found without actually combat scanning your target down. They may be in an anomaly, in which case d-scan is sufficient to find them. They may be in a scannable combat site, in which case a regular probe launcher is sufficient for the task. The only cases in which you need combat probes is to find mission runners, or if they have spotted you and are hiding in a safe spot. In the latter case, they will be alert for combat probes and aligned out in case they get close.