These are nice, small gold coins that are worth their weight in gold. They come in three denominations:
2.5 (dos y medio) pesos: 16 mm diameter, 0.060 troy ounces gold
5 (cinco) pesos: 19 mm diameter, 0.120 ounces gold
10 (diez) pesos: 22 mm diameter, 0.241 ounces gold
(Note: Gold 2 pesos coins from the same period look different than these coins. See their appraisal page at this link.)
To figure the value, go to Kitco.com and get the current spot value of gold. Then multiply that number by the number of troy ounces of gold in your coin. For instance, if spot gold is $1360 US dollars per ounce, and you have a dos y medio coin, the value is 0.060 x $1360 = $82 US dollars. A diez pesos coin would evaluate to 0.241 x $1360 = $328.
Remember, when dealing with precious metal, 'troy' is understood. So 'troy ounces' and 'ounces' mean the same thing.
These numbers give the value of just about all of these coins. But, there are some special pieces which are worth more.
For a 1947 dos y medio, add at least $200 US dollars due to rarity for an average circulated specimen, and add $700 for a fully uncirculated specimen.
For a 1905 cinco, add $70 for average circulated, and $500 for fully uncirculated coins.
For diez coins dated 1905, 1916, and 1920, add $150. The 1920 date is the most rare, having a premium above gold value of $700 in fully unciruclated condition.
For any fully uncirculated coin of this series, add $50, except for the 1945 dos y medio which is very common, as they have been restruck with the same date all the way up to 2009.
As always, problems with rare coins will detract from value. If you coin has scratches, for instance, and the scratches are severe, the value over spot value goes to zero.
NEVER CLEAN A COIN. CLEANING RUINS VALUE.