how to stop it letting me put it incorrect characters

[spazzirifick]

my challenge is to create a program to calculate the cost for a particular customer according to how many dogs they have to be washed.
1 dog = $10.00
2 Dogs = $17.00
3 or more Dogs = $17.00 (price for 2 dogs) + $5 for each additional dog.

i therefore have written the following code:
its not layed out correctly since i havent had time to fix it yet..please try and read through!

Option Explicit
 
Private Sub cmdamountfordwc_Click()
txtamountfordwc.Text = Format(txtcalculatedprice.Text * Val(0.05), "$0.00")
End Sub
Private Sub txtenterdognumber__KeyPress(KeyAscii As Integer)
    If KeyAscii < 48 Or KeyAscii > 57 Then
        Select Case KeyAscii
            Case 8
            Case Else
                KeyAscii = 0
            End Select
        End If
End Sub
 
Private Sub cmdCalculateCharge_Click()
If txtenterdognumber.Text >= 1 Then
txtcalculatedprice.Text = Format(Val(10), "$0.00")
 
 
End If
If txtenterdognumber.Text >= 2 Then
txtcalculatedprice.Text = Format(Val(17) + ((txtenterdognumber.Text - Val(2)) * Val(5)), "$0.00")
End If
If txtenterdognumber.Text = 0 Then
    Beep
    MsgBox "    PLEASE ENTER NUMBER OF DOGS    ", vbExclamation
    txtcalculatedprice.Text = "0"
    txtamountfordwc.Text = "0"
    
          
    End If
End Sub
 
Private Sub cmdclear_Click()
    txtamountfordwc.Text = ""
    txtcalculatedprice.Text = ""
    txtenterdognumber.Text = ""
End Sub
 
Private Sub cmdcountall_Click()
Call cmdCalculateCharge_Click
Call cmdamountfordwc_Click
End Sub
 
Private Sub cmdexit_Click()
End
End Sub
Private Sub txtcalculatedprice__KeyPress(KeyAscii As Integer)
    If KeyAscii < 48 Or KeyAscii > 57 Then
        Select Case KeyAscii
            Case 8
            Case Else
                KeyAscii = 0
            End Select
        End If
End Sub
Private Sub txtamountfordwc__KeyPress(KeyAscii As Integer)
    If KeyAscii < 48 Or KeyAscii > 57 Then
        Select Case KeyAscii
            Case 8
            Case Else
                KeyAscii = 0
            End Select
        End If
End Sub
 
Private Sub txtenterdognumber_Change()
If KeyAscii < 48 Or KeyAscii > 57 Then
        Select Case KeyAscii
            Case 8
            Case Else
                KeyAscii = 0
            End Select
        End If
End Sub

the problem is i have to stop it letting me enter letters into the box, or decimal points and multiple letters and to not let you type them in. as you can see i have tried to but it just doesnt want to work. what have i done wrong?