Difficulty in Determining Value
Apparently when it comes to ancient fishing and pricing, there is little to go by. One source referring to a different region of the Roman Empire (the Black Sea area) states of "epigraphic evidence" that "with one exception, we lack
evidence for a specific price charged for a definable quantity of salt-fish or
volume of fish sauce."1 On the same page is mentioned one piece of evidence (probably the "one exception") that gives pricing information in the Roman world, but it is almost three centuries after Christ.2
As such, it is not very useful, especially since pricing was by weight, not number. It was probably not like the picture of fish in a net on page 193 of this book, as the fish are really quite small. The Bible tells us the size of the fish here were μεγάλων ("large"), enough that the 153 of them together they could not haul into the boat itself (v.6), but could get it to shore (v.8, 11). Seven men were on the boat (v.2), but there is more than just manpower involved in trying to counter-balance a boat to haul in a net full of fish. But the actual weight is still unknown, as the size of the net is unknown, and "large" is a very non-descriptive term for weight (in many contexts a 12-24 inch fish might be large, but not as large as 36+ inches).
As such, there are just too many unknowns to "value" the fish here. It was probably of a reasonably good value for a haul of fish in that day, but too little is known to be sure.
Value is Probably the Wrong Focus
It is unlikely the value of these particular fish were a temptation to Peter. This is because the text would seem to point to them being a symbol and reminder of Christ's promise to Peter. Without Jesus telling them to cast to the other side at that moment (v.6), they would have remained without fish (v.5). The whole experience was reminiscent of Christ's earlier meeting with Peter (Luke 5:4-8), when Peter recognized his own weakness (5:8), but Christ promised to make Peter the fisher of men (5:10).
Now Jesus is calling Peter to that task. So when Jesus asks if Peter loves Him more than τούτων ("these") in v.15—a reference that is ambiguous in Greek gender, and so could be masculine (referring to the other men there) or neuter (referring to the fish)—I believe it is a reference to the fish, but not specifically these fish, nor their value, but rather the whole concept of "fishing" that was Peter's life prior to meeting Christ.
Will Peter give that up for love of Christ to "feed" His flock (vv.15-19)? Especially when considering that fishing may only be productive and lucrative if Christ is blessing Peter doing it (as evidenced in this story here); and the implication of Christ's commands are that He would not be blessing that life, but the one He was calling Peter to partake of—feeding Christ's people.
NOTES
1 Tønnes Bekker-Nielsen, ed., Ancient Fishing and Fish Processing in the Black Sea Region (Aarhus: Aarhus University Press, 2005), 43. (http://library.umac.mo/ebooks/b28050216.pdf accessed 5-2-2014)
2 That evidence is Diocletian's "Edict of Maximum Prices" which is from AD 301. The Edict is discussed in an accessible article, but for purposes here a summary of prices is laid out well here. In that summary, pricing is in "Denarii communes" which the source notes "were not actually silver denariias we usually think of when discussing ancient Roman coinage" but instead "were notational currency." Given that, "one libra" of fish (with "1 libra=326 grams or just under pound") were priced as such:
fresh-water fish were 12 (8 for 2nd quality)
salt-water fish were 25 (16 for 2nd quality)
So we can see a near double price for salt-water fish. That document notes a general laborer made about 25 a day, most skilled positions 50, so about a pound of fish could maximum be anywhere from half to a whole day's wages for the maximum of wages for lower to middle class type workers during the beginning of the 4th century. Maximum because that was what the edict was prescribing, the most that could be charged/paid.
