what is the minimum temperature that could be achived by a peltier fridge?

if want to make a fridge based on peltier effect , then what is the minimum deegre of temperature it could give me on the colder side?

Probably a little below freezing maybe 25 F or so. it really depends on the outside temp.
Any single stage Peltier will give you UP to around 45-50 Centigrade differential at ZERO power flow, or up to the rated power and ZERO temperature difference. So, in general if you say you can achieve half the temperature difference at half the power rating you have a handle on it. The power the device has to handle is determined by thermal leakage and by the energy stored in the item you're cooling.

Once its cold you only have to handle the thermal leakage. So GOOD insulation is a key.

If you want REALLY low temperatures, and power handling, you can stack cells up, but you need more/bigger cells in each subsequent layer. I have designed a research chiller that gets me -50C and can pump 10W. That takes THREE layers of cells, and consumes up to 400 W to do it.

I didn't add, that the efficiency of the cells falls with absolute temperature too, so my final cells in that stack lose 75% of their cooling ability.